Diarrhea is one of the most important causes of morbidity and mortality in countries with inadequate water sanitation, crowding and poverty. In this study we evaluated the rotavirus infection profile in Porto Alegre, Brazil. We analyzed the results of 603 laboratory tests obtained from patients who attended a private laboratory to investigate gastroenteritis during a 2 year period (from July 1996 to June 1998). Rotavirus was identified as the causative agent in 42/312 (13.4%) of patients during the first year, and in 55/291 (18.9%) during the second year. Coproculture for Salmonella and Shigela was positive in only 6.6% of the patients. The prevalence of rotavirus was significantly higher in the winter season and inversely related to the average temperature. Children 7 months to 18 months of age were the most common group infected with rotavirus. The presence of leukocytes in the feces did not correlate with the occurrence of this disease. These results agree with other studies concerning the age group, season, and overall prevalence of rotavirus. The results confirm the need for new approaches to the prevention, diagnoses and management of this disease.