Compliance with dietary recommendations and the effect of intensified dietary therapy on energy and nutrient intakes and fatty acid composition of serum lipids were studied in 86 obese subjects (aged 40 to 64 years) with recently diagnosed non-insulin-dependent diabetes mellitus (NIDDM). After three months of basic education, the subjects were randomly separated into an intervention group (n = 40) and a conventional treatment group (n = 46). Members of the intervention group participated in 12 months of intensified education; those in the conventional group visited local health centers. Compliance with dietary instructions was monitored through food records. Intensified dietary therapy resulted in greater weight loss, better metabolic control, and a less atherogenic lipid profile than conventional treatment. Intake of energy and saturated fatty acids tended to decline in the intervention group. A higher percentage of patients in the intervention group had a total fat intake of 30% of energy or less after 15 months (32.5% [12 of 38] vs 17.4% [8 of 46]). Similarly, more patients in the intervention group had a saturated fatty acid intake of 10% or less of total energy intake at the end of the study (35.0% [13 of 38] vs 8.7% [4 of 46]). The mean dietary cholesterol intake was within recommendations in both groups at the end of the study. The relative percentage of linoleic acid of serum lipids increased significantly and the relative percentage of palmitic acid of serum triglycerides, phospholipids, and cholesterol esters decreased in the intervention group. These changes indicate that intensified dietary therapy improved the quality of fat in the diet of patients with NIDDM.