The internal consistency, test-retest reliability and factor structure of the Castilian Spanish version of the 12-item General Health Questionnaire (GHQ) were studied with a sample of 1930 Spanish adolescents (M age=15.9 yr., SD=2.1). Cronbach alpha for the whole sample was .85 (.81 for boys, .87 for girls). Test-retest reliability was also satisfactory: r=.75 for boys, .81 for girls, .79 for the whole sample. After applying principal components factor analysis with varimax rotation, two factors were identified that jointly accounted for 46.8% of the total variance, Anxiety and Social Dysfunction. The results suggest that the GHQ-12 items is a questionnaire with some satisfactory psychometric properties.