To test the hypothesis that family function differs in patients according to their level of diabetes control, family function was assessed using the Family APGAR questionnaire in low-income patients with adult-onset diabetes who were under comprehensive care in five community health centers. From 3,000 active patients, a group of 385 with the following characteristics were randomly selected: mean age, 59.1 (range 25-93); M:F ratio, 1:4; and ethnic distribution (blacks: Hispanics: whites, 48%:31%:21%). Categorizing patients by their extent of diabetes control, good family function was found in 92% of patients in good control of their diabetes mellitus, in 66% of those in fair control, and only in 50% of those in poor control (p less than 0.005, chi 2 = 44.1, df = 2). Since these data point to the association between levels of family functioning and control of diabetes, further studies are needed to ascertain if an improvement in family functioning will lead to better diabetic control.