Although actuarial instruments are ubiquitously used in the field of sex offender recidivism risk assessment, there is limited empirical information about the underlying constructs from which they are derived. The following study utilized a nonparametric item response theory procedure, a Mokken analysis, and nonlinear factor analysis (Normal Ogive Harmonic Analysis Robust Method) to explore the underlying constructs of the STATIC-99 scores obtained for male sexual offenders (N = 451) referred for an evaluation to determine if they met criteria for civil commitment under a state’s Sexually Violent Persons Law. The results from the analyses indicated that the STATIC-99 comprises the two previously identified constructs associated with sexual deviancy and antisocial behaviors as well as a third, additional construct, associated with the items pertaining to age and past marital-type relationships. These findings support Hanson and Thornton’s assertion that sexual offender recidivism risk is multifactorial and not the result of a single underlying trait. Implications for future research are discussed.