Fifteen out of 24 risk neonates from the premature baby ward (= 63%) and 36 of 79 healthy neonates from the infant nursery (= 46%) at a Zurich hospital were infected within a period of 29 days during a nosocomial epidemic human rotavirus (HRV) outbreak. Forty-two out of 51 of all HRV-infected babies (=82%) manifested clinical symptoms, but these could not all be attributed to an HRV infection. On average, rotavirus could be detected in infected risk neonates five days after their admission to the premature baby ward. Eleven of the 15 risk neonates were infected within 10 days after the admission of the index case. Immediately after detection of the epidemic process, specific detailed countermeasures were instituted, including hand protection and hand disinfection, individual nursing set and cohorting of already infected babies. Early institution of such measures and information of all persons responsible for treatment and care of the babies concerned are crucial for success.