During the period of January 2003 to December 2005, 3,768 stool samples were received in the Microbiology Laboratory for rotavirus antigen detection from outpatients and inpatients of Albert Einstein Hospital, SP. Fresh stool samples from children and adults were analyzed by two methodologies: during 2003 and 2004 by latex agglutination (Slidex Rotavirus, Biomerieux) and 2005 by an immunochromatographic assay for the combined detection of rotavirus and adenovirus (Vikia Rota-Adeno, Biomerieux). Rotavirus group A was detected in 755 (20%) samples. The annual prevalence was 19.8% in 2003, 21.7% in 2004, and 18.7% in 2005. Rotavirus was detected every month during the period of the study, with peak of positivity between June and August (>35%). The prevalence in hospitalized patients was 26.1% (352/1,350) and in outpatients was 16.7% (403/2,418). For hospitalized patients most of the rotavirus infections were diagnosed in Pediatric setting, age range of 0 to 10 years (prevalence of 55.3%, 295/534). Overall positivity was up to 30% in patients between six months and five years of age (67% of all positive patients), all other age groups had at least 10% positive tests. Rotavirus infection is common in Sao Paulo, and besides the expected higher frequency in children it is also frequent in adults.