In the present article we describe a patient with AIDS and chylous ascites secondary to B-cell non Hodgkin's lymphoma. A 43 years old homosexual HIV-positive man. Complained of abdominal fullness, diarrhea and a rapidly increase in abdominal girth of 1 week duration. A diagnostic paracentesis was performed and revealed a milky fluid with high triglyceride levels. All blood tests and analysis of the peritoneal fluid with polymerase chain reaction for DNA sequence of broad-range bacterial Post Voiding Residual volume, Mycobacterium tuberculosis, Kaposi Sarcoma associated Herpes virus and Epstein Barr Virus were negative. CT scan did not demonstrate any evidence for cancer. An exploratory laparotomy was thus performed. A mass spreading along the mesenteric route to the omentum was found and a debulking resection was performed. The final pathology report was of diffuse, CD20-positive, CD3-negative, Epstein Barr Virus-negative, large B-Cell non Hodgkin's lymphoma. Subsequently, he underwent five cycles of CHOP (cyclofosfamide, doxorubicin, vincristin, prednison) chemotherapy with further partial regression of the abdominal tumour. Five months after the initial diagnosis of lymphoma, the patient relapsed and was treated with high-dose BEAM (carmustine, etoposide, cytosine, arabinoside, melphalan) chemotherapy followed by CD34 stem-cell transplantations salvage therapy. This notwithstanding, the patient died due to intestinal secondary to tumor relapse 2 months later.