Eating disorders caused by brain tumors are infrequently seen. Recent studies revealed that a neurocircuit from the nucleus tractus solitarius of the medulla oblongata to the hypothalamus participates in the control of appetite. Among brain tumors, those located in the brain stem, especially a solitary one in the medulla oblongata, are rare. Tumors in the brainstem are generally considered gliomas, and with the difficulty in reaching the lesion, treatment without histological confirmation is often performed. However, there are a few reported cases of medulla oblongata tumors other than gliomas. We describe a case of a 56-year-old man who presented with persistent anorexia. Magnetic resonance images revealed a solitary tumor in the medulla oblongata. After several examinations, craniotomy for the biopsy of the tumor using the cerebellomedullary fissure approach was carried out and primary central nervous system lymphoma (PCNSL) was histologically proven. The patient was treated with effective adjuvant therapy and was discharged home after he recovered from the symptoms. No tumor recurrence was recognized 24 months after surgery. A PCNSL arising only from the medulla oblongata is very rare, and anorexia can be an initial symptom of a tumor in the medulla oblongata. Surgical intervention is safely achieved and is a key to a better clinical outcome.