A 12-month epidemiologic study in 1979 and 1980 of all diabetic acidosis admissions to all acute care hospitals in Rhode Island detected 152 episodes occurring in 137 persons. Eleven per cent of diabetic acidosis admissions presented in coma and the overall death-to-case ratio was 9%. Newly diagnosed diabetes accounted for 20% of these episodes, while persons having multiple episodes during the year accounted for 15% of the admissions. The annual rate of diabetic acidosis was 46 per 10,000 diabetics. Highest rates of diabetic acidosis were found for the elderly, those admitted from nursing homes and those residing in one geographic area of the state. For known diabetics with an admission for acidosis, 87% were on insulin prior to admission and 81% were nonobese. Patients seldom contacted physicians prior to admission. Insulin dose or frequency was often (40%) changed in the two weeks prior to admission. Most of the known diabetic cases of acidosis had emergency admissions for diabetes in the three-year period prior to admission and few had any structured diabetic outpatient education. Infection and noncompliance were the most frequently identified precipitants of diabetic acidosis occurring in known diabetics.