Twenty five consecutive patients with fever of unknown origin (FUO) who underwent diagnostic laparatomy (DL) are reviewed. There were 14 females and 11 males, with a mean age of 34 years. The main symptoms and signs besides fever were malaise, weight loss, varied abdominal complaints, peripheral lymph nodes enlargement, hepatomegaly and splenomegaly. The main laboratory abnormalities were: anemia, leukocytosis, and mild alterations in liver function tests. CT scan was performed in 14 patients: hepatomegaly, splenomegaly and or retroperitoneal nodes were found in 10 of them. During laparotomy, an extensive exploration of intra-abdominal organs was performed, taking multiple biopsies for histopathologic and microbiologic analysis. Splenectomy was performed in 17 patients, prophylactic appendectomy in four, and cholecistectomy in one. Laparotomy was useful to establish a diagnosis in 64 percent of cases. The most frequently diagnosed pathologies were lymphoma and tuberculosis. Postoperative morbidity was 12% and mortality was 4%. Mean follow-up was 29 months. When preoperative data were analyzed, no predictive factors were found for a laparotomy with diagnostic success. It is concluded that DL is a useful last-step procedure in the diagnostic work-up for patients with FUO.