Aim. To assess whether visual perception of body mass correlates with objective body mass and whether the adequacy of a body percept is connected with losing weight. Materials and Methods. The research group consisted of 150 overweight adult women, participants of out-patient weight loss therapy. The silhouette test and the body mass assessment scale were used to measure body percept. Results. Self-estimation of body mass measured with the silhouette test was significantly adequate (X-2=64.027; P<0.001). The correlation between body mass reduction and the adequacy of perceived Body Mass Index (BMI) at the beginning of the therapy, appeared both in the assessment scale (R=0.176; P<0.05) and the silhouette test (R=0.207; P<0.05). A significant difference in the effectiveness of weight loss therapy between participants perceiving their initial body mass adequately and inadequately, appeared in the assessment scale (Z=-2.527; P<0.05) and in the silhouette test (Z=-2.152; P<0.05). Discussion. Body percept is influenced by many factors and the accuracy of body mass estimation affects the motivation to lose weight. Conclusions. Visual methods are more accurate in estimating subjective body mass than conceptual methods. There is a relation between the adequacy of initial body percept and the effectiveness of weight loss therapy.