The psychosocial correlates of glycemic control were examined in an incident cohort of childhood onset insulin-dependent diabetic subjects aged 18 years or older (n = 592). Glycosylated hemoglobin was measured at subjects' clinical examination, and questionnaires on diabetes self-care activity, barriers to regimen adherence and social support were completed. Demographic information was also collected. Glycosylated hemoglobin (GHb) was correlated with age, income and educational attainment (correlations coefficients between -0.1 and -0.2; P < 0.01), suggesting that older, more educated and wealthier patients have better glycemic control. GHb was also inversely associated with the degree of self-care activity (r = -0.11; P < 0.01), in particular administering injections at the recommended times and the frequency of performing blood/urine tests. Factors related to self-care behavior were identified, and included degree of social support (r = 0.14; P < 0.001) and patients' reports of difficulties adhering to their self-care regimen (r = -0.3; P < 0.0001). Gender was also related to self-care activities, with women reporting more self-care behavior than men (mean self-care scores 17.9 +/- 3.7 vs. 16.9 +/- 4.0; P < 0.01). Thus psychosocial factors (e.g. low income and education) may have an important effect on glycemic control in adults, and also (e.g. social support and adherence difficulties) seem particularly important in influencing the performance of self-care. As good metabolic control may help avoid the progression of diabetic complications, efforts need to be directed towards patients with these characteristics who are more likely to experience difficulties with self-care.