Several laboratory workers have demonstrated a viral agent, suspected of playing an important role in the aetiology of calf diarrhoea during the first weeks of life. Based on its morphology this agent was designated a Reo-like virus. Later the name Rotavirus was introduced. Rotaviruses were proved experimentally to induce diarrhoea in calves. Usually the course of the disease after similar experimental infection is mild, but could become worse with secondary bacterial infections. The available information on the virus itself, the clinical aspects of the infection, its pathogenesis, diagnosis, epidemiology and prevention are reviewed.