Background This study was to assess certain epidemiological and clinical characteristics of astrovirus infection in children with diarrhea below 5 years old hospitalized at the Beijing Children's Hospital. Methods From September 1999 to August 2001, a total of 288 children with diarrhea below 5 years old hospitalized at Beijing Children's Hospital were studied. Fecal specimens collected from each patient were tested for astrovirus by using enzyme immunoassay (EIA) and further serotyped by reverse-transcription polymerase chain reaction (RT-PCR) using serotype-specific primers. Results Astrovirus antigen was positive in 9.6% of the patients, and the rate of coinfection with rotavirus was 19.2% among the astrovirus positive patients. The patients with astrovirus infection were at the age of 7 days to 17 months, most (92.3%) of them were less than 12 months. Astrovirus infection occurred mainly between October and March of the following year. Main symptoms included watery stool, vomiting, fever, and dehydration. Increased activity of myocardial enzyme was seen in 4 patients. Of the 22 astrovirus positive specimens, 14 were successfully serotyped by RT-PCR and they were all serotype 1. Conclusions The overall incidence of astrovirus infection in young children with diarrhea hospitalized at the Beijing Children's Hospital was 9.0%. The predominant serotype was type 1. Astrovirus may play an important role in viral diarrhea in young children in Beijing, China.