Laboratory and hospitalization data from two children's hospitals with large primary catchment areas and national laboratory and hospitalization data for children under 4 y of age with acute diarrhoea were compiled to estimate the number of hospitalizations and the cost burden associated with rotavirus diarrhoea in Sweden. According to our estimates 1500-1700 rotavirus-associated hospitalizations occur annually in Sweden in children under 4 y of age (3.7 hospitalizations/1000 children/y). This number represents 2.3% of admissions for all diagnoses in children of this age group. The cost of these hospitalizations is 13.5-15 million Swedish crowns (US$1.8-2 million). Serotyping by PCR for two years revealed that serotype 1 (G1) was the most common (49% and 58%, respectively) identified. Serotypes 2-4 were identified in the following proportions G2 (23% and 5%), G3 (21% and 0%) and G4 (7% and 16%). The national laboratory report data for 1993-96 show that as much as 7-13% of rotavirus infections occur in elderly people.