The purpose of this study was to compare the effects of exercise and/or caloric restriction for 12 wk on body composition, maximal aerobic power (VO2max), and serum lipids and lipoproteins in overweight individuals. Forty-eight males and 48 females (&OV0398; age = 36.6 yr), 120–140% of ideal body weight, were randomly assigned to groups (N = 12 each) of diet-exercise (DE), diet (D), exercise (E), and sedentary control (C). The dietary regimen consisted of 1,200 kcal·d-1, while exercise consisted of 5 d·wk-1of 30 min of walk/ running. For the males, body weight (BW) and fat weight loss in the DE group (-11.8 and 23%, respectively) were significantly greater than in the D group (-9.1 and −18%), with both groups significantly greater than for E and C. In the females, BW and fat weight loss for DE (-10.4 and −24%) were significantly greater than for D (-7.8 and −20%), with both groups significantly greater than E and C. Both DE and D males and females had a decrease in fat-free weight of −4.5 and −2.4%, respectively. In both sexes, the increase in &OV0312;O2max-BW(ml·kg-1·min-1) in DE(25%) was significantly greater than for E (15%), D (11%), and C (0%), with differences between E and D nonsignificant. However, increases in absolute &OV0312;O2max(1·min-1) and &OV0312;O2max-fat-free weight (ml·kg-1·min-1) were similar (P≥ 0.05) for DE and E (14%) but significantly greater compared to D and C (2%). The DE males had significant decreases in total cholesterol and very low-density lipoprotein cholesterol after weeks 4, 8, and 12 and in triglycerides after weeks 8 and 12. In the DE females, triglycerides were significantly decreased after weeks 4 and 8. High-density lipoprotein cholesterol remained constant across time for all groups of males (35.8 ± 7.4 mg·dl-1) and females (47.8 ± 10.7 mg·dl-1), respectively. Thus, in overweight men and women, DE will produce a greater loss of BW and fat weight and a greater increase in &OV0312;O2maxcompared to D alone. High-density lipoprotein cholesterol is unaffected by diet and/or exercise, while triglycerides and very low-density lipoprotein cholesterol may be decreased.