A young girl who was only 17 years old came to the hospital with stomach pains for a week. When she came to the hospital, she had pain all over her stomach, most severely in her lower left abdomen, with diarrhea and vomiting. She began to consider the possibility of acute gastroenteritis, but the application of antibacterial drugs did not improve her symptoms, but worsened them. A CT examination was performed and an inflammatory mass was found in the left lower abdomen. Although the girl did not have fever, her systemic symptoms became increasingly severe, with shortness of breath and rapid heartbeat. Acute peritonitis was considered, but the cause was unclear, could it be intestinal perforation? In order to remove the inflammation in the abdominal cavity, we performed a caesarean section on her. During surgery, a large abscess was found in her left lower abdominal cavity and pelvis and extended to the right. Further investigation revealed that the source of the abscess was an appendiceal abscess and pelvic abscess caused by perforation of the appendix in acute appendicitis. She was operated on for abscess removal with appendectomy and pelvic drainage, and recovered quite well after the operation. Appendiceal abscesses and abdominal abscesses are usually seen in elderly and diabetic patients, but how could a young girl in her flowering season have such a large pelvic abscess caused by a common appendicitis? Generally speaking, young people are sensitive to pain and are usually seen and treated early. However, this young girl took painkillers from the beginning of her abdominal pain for a week, and then she came to the clinic only when the abdominal pain was too much. Originally, the appendix pain should be on the right side of the lower abdomen, but she had an abscess in the whole pelvis, and the left side was bigger, so the pain was shifted to the left. The symptoms were masked by prolonged pain medication and not treated in time, thus the inflammation spread to the entire abdominal cavity, which is really rare in today’s medical conditions. In general, painkillers should not be applied to pains where the cause of the abdomen is still unclear. The reason is that some parts of the abdomen are blind to examination, such as the small intestine, which is difficult to clarify by normal examination methods. Therefore, doctors usually adopt the method of observing the development of the disease while treating and doing the corresponding examination. The treatment is like a police officer solving a case, using the method of elimination to exclude suspicious diagnoses and gradually establish the final diagnosis. For such patients, if painkillers are applied, the doctor will not be able to see the development of the disease and the process of change, which will eventually lead to misdiagnosis and aggravation of the disease. There are two types of painkillers commonly used in abdominal pain surgery. One is systemic painkillers, including opiates and some non-steroidal drugs, such as morphine and aspirin, ibuprofen, etc., which can stop pain in all parts of the body. The other kind is drugs that release smooth muscle spasm in the gastrointestinal tract, such as atropine and scopolamine. The latter is not strictly a pain reliever, and can be used at the discretion of the patient with gastrointestinal spasm. However, for patients with abdominal pain whose etiology is not yet clear, the first type of painkillers should be used with caution. Nowadays, there are many pharmacies and it is convenient to buy medicines, so many people are used to seeing their own doctors and taking some medicines casually, which also brings a lot of safety hazards. Just like this little girl, taking some painkillers is good for the pain, but the problem is covered in the stomach, a small problem dragged into a major disease. Fortunately, she underwent surgery in time, but if it had been delayed any longer, it could have caused systemic sepsis and cardiopulmonary impairment, the consequences of which are unimaginable. Therefore, it is best to go to the hospital for abdominal pain whose cause is not yet clear, and do not take painkillers at will. The application of systemic painkillers must be cautious.