The present study was conducted between October 1996 and October 1998 to estimate the frequency of verocytotoxin-producing Escherichia coli among outpatients with diarrhoea in Switzerland. Among 3,041 subjects studied, 16 (0.5%) verocytotoxin-producing Escherichia coli infections were identified. Eleven cases were in infants and children </= 6 years of age. In 15 cases, a verocytotoxin-producing Escherichia coli strain was isolated. These strains belonged to 11 different serotypes, and only two were serogroup O157. In five cases, the infection was probably acquired outside Switzerland. Verocytotoxin-producing Escherichia coli apparently play a minor role in the aetiology of diarrhoeal disease in adult outpatients in Switzerland, but they are important pathogens in preschool children in whom the most severe symptoms are observed.