To evaluate the efficacy of conventional diabetes care in a rural area, metabolic control and the presence of late complications were studied in 622 diabetic patients treated by general practitioners beyond the reach of diabetic centers. Seventy-three (12%) of the patients were classified as type I diabetics (age, 38.0 +/- 16.1 yr; duration of diabetes, 12.8 +/- 9.3 yr) and 549 as type II diabetics (age, 67.0 +/- 10.8 yr; duration of diabetes, 7.3 +/- 5.8 yr). Fifty-eight percent of type I diabetic patients administered insulin once daily and 42% twice daily, whereas most (83%) type II diabetics on insulin received only one insulin injection per day. Treatment of type II diabetic patients consisted of sulfonylureas (58%), diet alone (22%), insulin (18%), and biguanides or a combination of sulfonylurea with biguanides (2%). Poor therapeutic efficacy was observed in all patients, and postprandial hyperglycemia (blood glucose greater than 160 mg/dl) was predominant both in type I diabetics (86%) and in type II diabetics on insulin (80%) as well as off insulin (55%). HbA1c above normal (greater than 5.8%) was seen in 96% of type I and in 90 and 73% of type II diabetics with or without insulin therapy, respectively. Accompanying glucosuria was present in type I (73%) and in type II diabetics (on insulin, 71%; off insulin, 33%). Mean prevalence of late diabetic complications was greatest for insulin-treated patients (type I, type II with, and type II without insulin treatment: retinopathy, 41, 56, 22%; proteinuria, 13, 14, 3%; peripheral neuropathy, 21, 51, 12%), whereas macroangiopathy (16, 53, 31%) predominated in type II diabetic patients.(ABSTRACT TRUNCATED AT 250 WORDS)