A statewide insulin-dependent diabetes mellitus (IDDM) registry is used to identify and epidemiologically characterize patients admitted to Rhode Island's hospitals. Physician interviews and record reviews are obtained to ascertain reasons for hospitalization. Poor diabetes control (noncompliance with diet/medication) and infection accounted for 44-54% of hospital admissions among 691 known diabetic patients; these patients were readmitted more often (65%) compared with new-onset patients (46%) during a 3-yr follow-up of hospitalization patterns. An outpatient diabetic education program was successful in reducing the number of persons hospitalized (P = 0.04) and the number of hospitalizations for participants (P = 0.01) when comparisons of hospital admissions before and after the program were made. Potential cost savings for persons with IDDM over the 4 yr of the study are estimated at $674,400.00.