This study evaluated the psychological effects of aerobic conditioning in 40 moderately obese, sedentary women participating in a 12-week behavioral weight loss program. Participants were randomly assigned to a no-exercise or moderate walking condition. Emotional impact of the treatment was assessed in two ways: (1) Subjects reported subjective mood prior to each eating episode and (2) the SCL-90-R was administered before and after the program. Exercisers lost more weight and body fat than non-exercisers. Both groups of subjects showed numerous improvements in mood as a result of participating in the weight loss program. Exercise had no specific differential effect on emotions as measured by daily mood ratings or the SCL-90-R. Exercise did not appear to add appreciably to the psychological benefits of losing weight in this sedentary obese population. Future studies utilizing longer periods of aerobic exercise training, larger sample size, and exercise specific measures are recommended.