Eighty-five 12-18-yr-old adolescents suffering from insulin-dependent diabetes mellitus (IDDM) and their healthy age- and sex-matched controls were investigated with respect to dental caries, salivary flow rate, pH and buffering capacity of saliva, counts for lactobacilli and mutans streptococci, and salivary glucose content. The diabetics had their disease well controlled according to the HbA1 levels. The results showed no statistically significant difference between diabetics and controls in DMF and DMFS indexes and the number of initial caries lesions. Mean number of initial caries lesions was 3.2 in diabetics, 2.3 in controls. Mean stimulated salivary flow rate was 1.2 ml/min in the patients, 1.4 ml/min in the controls. The pH and buffering capacity values were 7.3 and 4.8 in the patients, 7.4 and 5.1 in the controls, respectively. High counts of mutans streptococci (> 10(6) CFU/ml) and lactobacilli (> 10(5) CFU/ml) were observed more often, but not significantly so, among the patients than in the controls. The mean concentration of glucose in saliva was 10.3 micrograms/ml in the patients, 9.7 1 microgram/ml in the controls. Thus, if the patients' IDDM is well controlled, their salivary and caries data does not differ from that of healthy controls.