This study examined the effectiveness of the addition of a cognitive intervention based on individualized assessment to a behavioral intervention. Sixty-three subjects who were at least 15% overweight were randomly assigned to a behavioral intervention or a behavioral intervention and a cognitive intervention focused on changing specific maladaptive self-statements related to weight loss. It was predicted that the behavioral and cognitive intervention would result in greater weight loss and reduction in body fat than the behavioral alone intervention at posttest and at 3-month follow-up; results did not support this hypothesis. Support was found for the construct validity of the behavioral intervention with significant differences between time points on behavioral measures observed. On the cognitive measures, both treatment conditions showed changes over time on cognitive measures, but differences between the treatments were not significant. Based on the results of this study, it is suggested that future research examining the effectiveness of cognitive interventions in the area of weight loss include measures other than those that are weight-related, longer follow-ups to assess long-term maintenance, and sufficient amounts of cognitive therapy so that clients have fully integrated the newly learned cognitive dialogues into their everyday lives.