OBJECTIVE: Clinicians need brief and valid instruments to monitor the psychosocial impact of weight gain in persons with psychiatric disorders. We examined the psychometric properties of the Spanish version of the Body Weight, Image and Self-Esteem Evaluation (B-WISE) questionnaire in patients with severe mental disorders. METHOD: The data come from a naturalistic, cross-sectional, validation study conducted at 6 centres in Spain. A total of 211 outpatients with severe mental disorders, 118 with schizophrenia and 93 with bipolar disorder, were evaluated using the B-WISE, the Visual Analogue Scale for Weight and Body Image, and the Clinical Global Impression-Severity (CGI-S). The body mass index was also obtained. RESULTS: The principal component analysis confirms 3 components explaining 50.93% of the variance. The Cronbach α values for B-WISE scales ranged between .55 and .73. Significant Pearson correlations were found between B-WISE total score and CGI-S (r = -0.25; P < .001) and Visual Analogue Scale for Weight and Body Image (r = 0.47; P < .001). The B-WISE discriminates among patients with mild, moderate, and severe mental disorders according to CGI-S scores (F = 6.52; P < .005). Body mass index categorization significantly influenced total B-WISE scores (F = 3.586, P < .050). The B-WISE score corresponding to the 5th and 10th percentiles was 22. CONCLUSIONS: We were able to demonstrate that the Spanish version of the B-WISE is a valid instrument for assessing psychosocial impact of weight gain in patients with severe mental disorders in daily clinical practice.