The study evaluated reliability, measured by Cronbach’s coefficient alpha, and concurrent validity, measured by Pearson’s r and polychoric correlation coefficients. The study assessed 371 sex offenders’ sexual interests and behaviors using the SI, a self-report measure of deviant and nondeviant sexual interest, as well as indicator variables obtained from classifications assigned as a result of two hour-long semistructured clinical interviews. The study established reliability and validity of the SI and a shortened version (SIS) in the measurement of deviant and sexual interests and behaviors in offenders, along with the ease of administering both questionnaires to clients within clinical environments. Both the SI and SIS assessed desire or repulsion toward multiple sexual behaviors and reliably distinguished deviant sexual interests and behaviors within individual offenders. Although the SI and SIS were reliable and valid, they should not be used outside the context of a broad assessment that incorporates other self-report measures, objective measures, criminal justice records, and data gathered from clinical interviews. Tables, references, appendix