A retrospective analysis was performed on 70 patients with diabetes mellitus who required nutritional support over the 10-yr period 1979-1989. Information was available for 65 patients, of whom 55 had non-insulin-dependent diabetes mellitus (NIDDM). Enteral nutrition (EN, 750-2200 kcal/day) was given to 40 NIDDM patients (group A) and 6 insulin-dependent diabetic (IDDM) patients (group B), and parenteral nutrition (PN, 1600-2400 kcal/day) was given to 18 NIDDM patients (group C) and 4 IDDM patients (group D). Three NIDDM patients required both types of feeding. Preadmission diabetes treatment remained the same during feeding for 31% of the total group (38% of group A, 33% of group B, 23% of group C, and 0% of group D). The NIDDM patients in group C who received insulin during PN required a high daily dose of approximately 100 U. The IDDM patients on PN required an increase of 225% from their preadmission daily dose. The likelihood of a patient requiring a major change from preadmission diabetes therapy depended mainly on the severity of the underlying illness and on the type of feeding (greater with PN) but not on preadmission therapy, age of patient, or type of EN (cyclic vs. continuous). Hypoglycemic episodes were uncommon in all groups. There were no significant differences between the prefeeding and feeding blood glucose levels and HbA1c results.