Oral carriage of Candida albicans was studied in 55 children and adolescents with Down's syndrome (DS), aged between 7 months and 20 years 6 months, and compared with an age- and sex-matched control group of subjects. Twenty-two of the DS subjects were diagnosed as having congenital cardiovascular malformations. Compared to controls, the DS subjects were more prone to infections. The number of subjects colonized with C. albicans in the oral cavity was significantly higher in the DS group (69%) than in the control group (35%). Colonization with C. albicans and simultaneous erythematous or white pseudomembranous lesions of the oral mucosa were diagnosed in 22 (40%) of the DS groups and in only one of the control group. In both the DS and the healthy control subjects the frequency of colonization with C. albicans was positively correlated to age. The DS subjects were significantly more densely colonized by C. albicans than the controls. Abnormalities of the immune response in DS children may contribute to the increased oral carriage of C. albicans.