OBJECTIVE To describe clinical symptoms of sporadic cases of noro- and astroviral infection in adults; to compare a clinical picture and a course of rotaviral infection (R VI), noroviral infection (NVI) and astroviral infection (A VI). METHODS Reverse transcription and polymerase chain reaction (RT-PCR) method was used to examine fecal samples from 1032 patients with acute intestinal infections (All) at the age of 15 to 90 years admitted to the infectious department of the clinic of Chelyabinsk State Medical Academy in 2004-2005. Detectability and severity of some symptoms in R VI, NVI and A VI patients were analysed and clinical manifestations of viral intestinal monoinfections were compared. RESULTS Monoinfection was diagnosed in 230 (22.3 %)fecal samples: RVI (n = 101), NVI (n = 100), A VI (n = 29). Sporadic morbidity was the highest from March to May, March to September, October to December for R VI, NVI and A VI, respectively. Gastroenteritis syndrome was prevalent in all the infections studied. Diarrhea with marked dehydration was more typical for RVI, dyspepsia and abdominal pain--for NVI. Intoxication occurred with the same frequency in all the infections. Severe RVI ran with normal body temperature in many patients over 60 years of age. CONCLUSIONS Viral diarrheal diseases are frequent in adults of all ages and run with similar clinical picture. The most serious course of the infection with most severe syndromes of gastroenteritis and dehydration was typical for RVI. Etiological nature of viral intestinal infections can be established only with laboratory diagnostic methods.