To assess the prevalence of Candida albicans and oral infection with Candida in patients with insulin-dependent diabetes mellitus (IDDM). This cross-sectional study compared the prevalence of candidiasis in 405 subjects with IDDM and 268 nondiabetic control subjects. Assessments included evidence of clinical manifestations of candidiasis and a quantitative measure of Candida pseudohyphae in a cytologic smear from the midline posterior dorsal tongue. More subjects with IDDM than control subjects without IDDM (15.1% vs 3.0%) were found to have clinical manifestations of candidiasis, including median rhomboid glossitis, denture stomatitis, and angular cheilitis. IDDM subjects were also more likely to have any Candida pseudohyphae in their cytologic smears (23.0% vs 5.7%; P 10/cm(2) (7.1% vs 0.8%; P <.0001). Diabetic subjects with median rhomboid glossitis were more likely to have a longer duration of IDDM and complications of nephropathy and retinopathy. Denture stomatitis was associated with smoking, retinopathy, higher Candida counts, poor glycemic control, and longer duration of IDDM. A multivariate regression analysis found 3 factors to be significantly associated with the presence of Candida pseudohyphae in the subjects with IDDM: current use of cigarettes (odds ratio, 2:4), use of dentures (odds ratio, 2:3), and elevated levels of glycosylated hemoglobin (odds ratio, 1:9). The use of antimicrobials, immunosuppressants, or drugs with xerostomic side effects was not related to the presence of Candida. Candida pseudohyphae and oral soft tissue manifestations of candidiasis were more prevalent in subjects with IDDM than in control subjects without diabetes. The presence of Candida pseudohyphae was significantly associated with cigarette smoking, use of dentures, and poor glycemic control.