We examined the epidemiological profile of rotavirus infection among children hospitalized for diarrhea in Taiwan, to assess the burden of this disease. From 1 April 2001 through 31 March 2003, children <5 years old with gastroenteritis admitted to 4 sentinel hospitals were enrolled in a surveillance study and had stool specimens tested for the presence of rotavirus, enteric adenovirus, and the bacterial pathogens for which routine screening is performed. For 52% of patients, a recognized enteric pathogen was identified, including rotavirus (43% of patients), bacteria (11%), enteric adenovirus (2.5%), and a mixture of pathogens (3.9%). Rotavirus was detected year-round, but great month-to-month variability made it difficult to identify a distinct seasonal pattern. Rotavirus disease was most common among children 7-23 months old, but the rate of rotavirus detection varied little between the youngest and oldest age groups. The novel strain PG9 was detected most commonly (37% of strains), followed by strains PG1 (31%), PG2 (10%), PG3 (9.3%), and PG4 (3.7%). Rotavirus infection is the most important cause of diarrhea among hospitalized children in Taiwan, and a rotavirus vaccination program for young children might significantly reduce this problem.