Underreporting of energy intake is a serious and pervasive problem, especially among women with overweight and obesity. The aim of this study was to determine if the prevalence and severity of underreporting changed after participating in a behavioral weight-loss program. Women with overweight and obesity (N=156, mean age 39.4 years, mean body mass index 31.9) completed a 6-month behavioral weight-loss program. Basal metabolic rate, physical activity level, and energy intake from 7-day food records were collected at baseline and 6 months. The major finding was that underreporting significantly increased in prevalence (39.7% vs 60.3%; P<.001), as did severity of misreporting (-105+/-583 vs -415+/-504 kcal/day; P<.001) following the behavioral weight-loss program. Thus, after completing a behavioral weight-loss program, the prevalence of underreporting and severity of misreporting became significantly worse among women with overweight and obesity.