Precocious puberty in boys is mostly peripheral, and the vast majority of them are triggered by hcg-secreting tumors. Confirmation and localization of the responsible lesion plays a decisive role in its treatment (tumors occurring in the testes can be detected by general physical examination, so they are not discussed here). The tumors responsible for precocious puberty in boys are concentrated in the central nervous system and are basically germ cell tumors. Early detection and treatment of the responsible tumor is of great significance to the prognosis of the child. Biochemistry combined with imaging examination is decisive for the diagnosis of this disease. I have experienced the diagnosis of several cases of precocious puberty in boys in recent years and found that it is difficult to diagnose precocious puberty in boys in time, and the longest delay is more than 2 years. The main reason for the delay in diagnosis is the lack of basic understanding of the disease, as well as insufficient knowledge of its imaging manifestations. The diagnosis of peripheral precocious puberty can be made based on clinical manifestations and abnormal increase in plasma hcg. Imaging examinations, which are responsible for the confirmation and localization of the lesion, are best performed by MRI among many methods. The scanning examination of the central nervous system is the first. Germ cell tumors, mostly in the pineal and basal ganglia regions, and rarely in the spinal cord. When reading the MRI of the head of a boy with precocious puberty, we should focus on the above-mentioned areas, otherwise it is very easy to miss the diagnosis. There have been three consecutive cases of precocious boys from a province (one case each from the provincial hospital, the city’s first hospital, and the university-affiliated children’s hospital) with a large stack of imaging data, but no lesions were found. Two cases were pineal gland tumors, which were relatively small in size but could be detected if attention was paid. One case was from the basal ganglia region, but unfortunately, MRI was done only for T1WI coronal and sagittal planes in the saddle area and reported normal; however, one coronal image showed increased signal in the right bean nucleus, which was found to be a calcified lesion in the right basal ganglia region (later confirmed to be a germ cell tumor) after further brain CT and MRI at our hospital. MRI scan of the whole spinal cord was also necessary to confirm that the brain was normal. Imaging workup of boys with precocious puberty was performed until the responsible lesion was found.