Between the March and May of 2000, stool specimens were collected from children aged <5 in six pre-school crèches and clinics in the Jeddah area of Saudi Arabia. Sixty-three (25%) of the children had diarrhoeal disease but the other 190 were asymptomatic. When the stool samples were stained and examined for the oocysts of Cryptosporidium spp. and other enteric protozoa, 20 (32%) of the symptomatic children but only nine (4.7%) of the asymptomatic were found to be excreting Cryptosporidium oocysts. Similarly, Cyclospora cayetanensis was found, always as a co-infection with Cryptosporidium sp., in seven (11%) of the children with diarrhoeal disease but only eight (4.2%) of the asymptomatics. One asymptomatic child was found to be co-infected with Isospora belli and Cryptosporidium. Giardia intestinalis and cysts of Entamoeba histolytica/dispar were detected in 18 (29%) and nine (14%) of the children with diarrhoeal disease and in eight (4.2%) and 13 (6.8%) of the asymptomatic children, respectively. This appears to be the first report of Cy. cayetanensis from Saudi Arabia and the highest prevalence of Cryptosporidium infection ever described.