The impact of sexual fantasies in future risk and treatment response among sexual offenders has long been known. However, as we develop objective self-report measures of sexual fantasies, response bias is becoming an increasing concern. In examining a sample of institutionalized sex offenders, the present study suggests that offenders’ responses on these measures are prone to response bias, the bias does not negate their associations with other self-report measures of sexual deviance, and relationship of their sexual fantasies does not appear to relate to actual behavioral indications. Clinical and research implications for these findings are discussed.