The present study examined the construct validity of the Violence Risk Scale–Sexual Offender version (VRS-SO) through an examination of its factor structure and convergence with psychological measures assessing conceptually relevant constructs in a sample of 732 treated incarcerated adult male sex offenders. The VRS-SO was rated prospectively pre- and posttreatment by service providers, and several of the men had completed a psychometric battery at each time point. Prospective Stable 2000 ratings were examined for comparison purposes. Results of exploratory longitudinal factor analysis, performed on VRS-SO pre- and posttreatment dynamic item scores, supported a three-factor model (comparative fit index = .990) and the measurement invariance of the loadings over time. A stringent longitudinal confirmatory factor analysis of the VRS-SO items also supported the three-factor structure. Scores from the three factors (Sexual Deviance, Criminality, and Treatment Responsivity) were correlated in conceptually meaningful ways with scores from the Stable 2000 and selected psychometric measures. The results provide evidence for the construct validity of VRS-SO test scores as providing an index of sex offender risk and, more specifically, that its item content and factor domains measure psychological constructs pertinent to sex offender risk and need.