This paper describes four studies on self-reported problems in 2,243 adolescent males and females, 12 to 17 years of age. In Study 1, principal-axis factoring of 102 items covering 11 problem domains revealed six factors comprising 49.5% of the variance. Study 2 used confirmatory factor analysis of a 64-item reduced set on a new sample of 408 adolescents. Goodness-of-fit indicators suggested that the six-factor model had excellent fit to the data. Study 3 used data from the 2,157 adolescents used in the first two studies. Coefficient alphas ranged from .83 to .92. Median test-retest reliability for the six factors was .86. There was a consistent structure of the correlation matrix across age and gender. Study 4 was a study of criterion validity, using an additional sample of 86 children with attention-deficit hyperactivity disorder (ADHD). Sensitivity and specificity were high, with an overall diagnostic efficiency of 83%. This new self-report scale, the Conners/Wells Adolescent Self-Report of Symptoms (CASS), may provide a useful component of a multimodal assessment of adolescent psychopathology.