Based on the potential clinical and research value of a measure of confidence in dieting, this study applied the principles of Self-Efficacy Theory to the validation of the previously developed Dieting Self-Efficacy Test (DSET). The DSET is a 30-item, paper and pencil measure of the ability to control dieting behaviors. In the current study, data were collected from two subject populations, a student group (N = 214) and an adult group (N = 237). Across a variety of sub-groups, DSET scores were related in a predictable manner to differences in subject's perceptions of their ideal weights. Specifically, high DSET scores were associated with being near-normal weight, while low DSET scores were associated with being overweight. Data analyses showed no major differences between the two groups, suggesting that age is an irrelevant factor in determining dieting self-efficacy. In addition, DSET scores from a substance-abuse recovery group were similar to a non-abusing group. Thus, substance-abuse was also determined to be an irrelevant factor. Further, DSET scores were shown to be unrelated to factors that influenced scores on a general self-efficacy measure. These analyses supported the construct and discriminant validity of the instrument. Significant differences were found between scores of males and females, with males scoring consistently higher than females. These differences were attributed to a feminine desire for thinness as explained by feminist theories of weight satisfaction. Consistent with the DSM-III-R bulimia nervosa criterion of a feeling of lack of control in eating, bulimics were shown to score considerably lower on the measure than non-bulimics. Finally, as predicted by self-efficacy theory, repetitive dieters who failed to achieve or maintain their ideal weights scored lower on the DSET than their non-dieting counterparts. As in the initial development study, the DSET was found to have high internal consistency (0.96). This study supported the DSET as a reliable and valid instrument for quantifying dieting self-efficacy.