Primary extranodal lymphoma starts in any tissue or organ outside the lymph nodes, and its main lesion is outside the lymph nodes. The clinical characteristics of primary extranodal lymphoma are related to the site of the lesion, and its clinical manifestations are diverse and lack of specific symptoms and signs, which can easily lead to misdiagnosis or underdiagnosis and directly affect timely and reasonable treatment. For this reason, we retrospectively analyzed 139 cases of primary extranodal lymphoma in terms of various sites and first manifestations to draw attention to extranodal lymphoma. 1. Data and methods 1.1 A total of 458 cases of lymphoma were hospitalized in Peking University First Hospital from December 1976 to February 2002, with 139 cases of primary extranodal lymphoma. Among them, 84 cases were male and 55 cases were female. The median age was 47 years (8 years to 89 years). All cases were clearly diagnosed by pathological biopsy. 1.2 The distribution sites and first clinical manifestations of 139 cases of primary extranodal lymphoma were analyzed retrospectively. 2. Results 2.1 Among 458 patients with lymphoma hospitalized in Peking University First Hospital from December 1976 to February 2002, 139 cases (30.3%) had primary extranodal lymphoma. 2.2 Among the 139 cases of primary extranodal lymphoma: 136 cases of non-Hodgkin’s lymphoma (NHL) and 3 cases of Hodgkin’s disease; among the 136 cases of extranodal NHL: 133 cases were diffuse and 3 cases were follicular. 2.3 The primary sites of extranodal lymphoma were widely distributed throughout the body, and the distribution of common primary sites was as follows: 29 cases in the gastrointestinal tract (including 15 cases in the stomach, 5 cases in the small intestine, 4 cases in the ileocecal region, 4 cases in the colon, and 1 case in the rectum), 26 cases in the nasal cavity, 18 cases in Waldeyer’s ring (14 cases in the tonsils and 4 cases in the pharynx), 15 cases in the spleen, 9 cases in the skin, 8 cases in the central nervous system, 6 cases in the oral cavity The pleura was found in 5 cases, and the thymus in 4 cases. The rare primary sites were: soft tissue in 3 cases, lung in 3 cases, testis in 2 cases, thyroid in 2 cases, liver in 1 case, pancreas in 1 case, gallbladder in 1 case, maxilla in 1 case, kidney in 1 case, prostate in 1 case, breast in 1 case, adrenal in 1 case, and larynx in 1 case. 2.4 The top 5 most common sites of primary extranodal lymphoma were, in order: gastrointestinal tract 20.9% (29/139), nasal cavity 18.7% (26/139), Waldeyer’s ring 12.9% (18/139), spleen 10.8% (15/139), and skin 6.5% (9/139). 2.5 Extra-nodal lymphoma is easily misdiagnosed. Gastrointestinal lymphoma is easily misdiagnosed as gastritis, gastric cancer, gastric ulcer, Crohn’s disease, ulcerative colitis, intestinal tuberculosis, colon cancer, etc. Nasopharyngeal lymphoma is easily misdiagnosed as sinusitis, rhinitis, nasal polyp, nasopharyngeal cancer, pharyngitis, etc. 2.6 The first symptoms of extranodal lymphoma have different clinical manifestations according to different sites, but most of them are not specific. The first symptoms of common sites are as follows: abdominal pain in 21 cases, abdominal distension in 5 cases, wasting in 4 cases, poor appetite in 3 cases, purulent stools in 3 cases, nausea and vomiting in 1 case. Nasal lymphoma manifested as: nasal congestion in 19 cases, runny nose in 8 cases, and fever in 3 cases. Among 2.7139 cases, 43 patients showed the following first signs: unexplained splenomegaly in 12 cases, tonsillar swelling in 10 cases, skin swelling or nodule in 7 cases, soft tissue swelling in 3 cases, tongue root swelling in 3 cases, thyroid swelling in 2 cases, painless testicular enlargement in 2 cases, abdominal swelling in 2 cases, pelvic swelling in 1 case, and breast swelling in 1 case. These signs should be detected and biopsied as soon as possible. The incidence of extranodal lymphoma: 25% in North America, nearly 50% in Europe, and 30.3% in this group. Therefore, extranodal lymphoma is not uncommon. The top 5 most common sites of extranodal lymphoma are gastrointestinal tract, Waldeyer’s ring, skin, central nervous system, and soft tissues, as reported abroad. In our data, the top 5 primary sites were gastrointestinal tract, nasal cavity, Waldeyer’s ring, spleen, and skin. The reasons for misdiagnosis of extranodal lymphoma are: (1) the primary sites of extranodal lymphoma are widely distributed and can occur in almost all parts of the body; (2) the primary clinical manifestations are often non-specific; and (3) the clinical experience of doctors is insufficient. Therefore, the misdiagnosis rate of extranodal lymphoma is much higher than that of intra-nodal lymphoma, and the clinic should be more alert to the primary extranodal lymphoma. In our data, gastrointestinal lymphoma is mostly manifested by abdominal pain and distension, which are not specific. Early detection of early cases can be achieved by early gastroscopy and biopsy, and Valentini M [6] found that 16.3% (10/61) of cases were normal to the naked eye but histologically confirmed with mucosal lymphoma invasion. Nasal lymphoma with nasal congestion and runny nose as the first manifestation should be biopsied as early as possible to exclude the possibility of lymphoma. For long-term unexplained fever, wasting and neurological symptoms, the lesions should be carefully searched for and the diagnosis should be confirmed as early as possible. Surgical excision of the lesion and pathological examination are the only means to confirm the diagnosis of the disease, and the following suspicious cases should be diagnosed by surgical biopsy pathology as soon as possible: (1) tonsils are often exogenous growths, and patients feel foreign body sensation and pain in the pharynx; (2) for soft tissue masses, tongue root masses, skin masses or nodular lesions; (3) for unexplained, especially progressive splenomegaly, if accompanied by unexplained fever or occupying lesions in the spleen by ultrasound ④ for unexplained abdominal masses and pelvic masses; ⑤ for painless testicular enlargement; ⑥ for masses in the thyroid and thymus areas, the possibility of lymphoma should be considered. In the above cases, if there is difficulty in pathological diagnosis, further genetic testing will be helpful for early and clear diagnosis.