A principal components factor analysis (with varimax rotation) was performed on the Millon Adolescent Personality Scale Base Rate scores of 335 adolescent psychiatric inpatients. A four-factor solution was obtained (accounting for 84.1% of the variance), which was similar to that obtained by Millon, et al, for the normative sample. Confirmatory factor analyses, however, using data obtained from computer generated random responses to the test, also fit the inpatient and normative sample data very well. The factor structure of the Millon Adolescent Personality Inventory therefore was inferred to be driven by the considerable item-scale overlap that characterizes the test.