This study analyzed the validity of the Sherer, et al. Self-efficacy Scale for a Spanish sample of 555 subjects, 257 men and 298 women. 415 were from the general population; 34 schizophrenics and 45 with eating disorders were from a clinic, plus 61 drug addicts from two centers. All met DSM-IV-R criteria. The Eysenck Personality Questionnaire, State-Trait Anxiety Inventory, Assertiveness Inventory, and the Self-control Questionnaire were administered. The reliability for total scores, general factor were high even when social self-efficacy was low. A bidimensional factor structure seemed more acceptable. The Self-efficacy scale scores correlated with those on the Self-control Questionnaire and the Assertiveness Inventory. Extraversion scores on the Sincerity dimension of the Eysenck Personality Questionnaire correlated with scores on the State-Trait Anxiety Inventory and Eysenck's Neuroticism and Psychoticism scales. Significant mean differences appeared between the general population group and the three clinical groups. These analyses support the usefulness of the scale for clinical practice and research with Spanish samples.