It has generally been assumed that oral candidiasis occurs with increased frequency in patients with diabetes mellitus. To evaluate this, we compared the frequency and severity of oral Candida colonization in 60 patients with insulin-dependent diabetes mellitus (IDDM) admitted to a low-intensity-care diabetes unit with those in 57 age- and sex-matched controls. Swabs taken from the tongue and buccal mucosa were examined by cytology rather than culture because of the discrimination provided by the former. Cytological smears were classified according to the presence and morphology of the Candida organisms. Overall, a significant difference in Candida species colonization was found between patients with diabetes (75.0%) and controls (35.1%) (p < .005). In the diabetic group, no relationship was found to recent use of antibiotics, total or differential white blood cell count, serum glucose, presence of diabetic retinopathy, or glycosylated hemoglobin values. We conclude that in IDDM there is a predisposition to oral candidiasis and that this predisposition is independent of glucose control.