The study monitored sex offenders on probation over time to assess recidivism and the predictive accuracy of SOTIPS. Probation officers in the two study sites completed SOTIPS at three time points: intake (start of probation), 6 months later, and 12 months later. Data were collected on probationers' residence and employment stability, terminations or transfers of probation, attendance at sex offender-specific treatment, and contacts between offenders and probation officers. Criminal record checks were done in the last year of this 5-year study. The overall finding is that SOTIPS is a promising instrument for assessing dynamic risk factors for sex offenders on probation. It showed good internal consistency and inter-rater reliability, as well as significant incremental validity when combined with Static-99R, the most widely used actuarial risk-assessment tool for sex offenders. The addition of SOTIPS scores at baseline, 6 months, and 12 months added information to the actuarial risk tool (Static-99R) and improved its predictive accuracy. These findings suggest that the best strategy is to administer SOTIPS at regular intervals during supervision or treatment. If this is not possible, SOTIPS administered closer to the release date would provide better prediction. The formative evaluation of the implementation of SOTIPS provided important insights for future research and the process of implementing new procedures within large governmental institutions. 12 tables, 2 figures, 28 references, and appended study materials