The aim of the study was to evaluate and to improve the decision-making algorithms that have been generated to assess risk in sexual offenders. More specifically, it was the task of this research project to evaluate the extant actuarials in a sample of sexual offenders on whom long-term follow-up data were available. Researchers attempted to assess the comparative accuracy of the major risk instruments over time and over subsamples, explore their underlying factor structure, examine the accuracy of a new assessment protocol, and explore the potential for generating improved predictive instruments. The sample was drawn from an earlier study in which researchers had followed 599 offenders who had been referred to the Massachusetts Treatment Center (MTC) for evaluation between 1959 and 1984. Of these, 266 (the Bridgewater Treatment [BT] sample) had been committed to MTC as "sexually dangerous" and subsequently released, and 333 (the Bridgewater Observation [BO] sample) had been determined not to be sexually dangerous and returned to finish their sentences. There were two sources of data for the study. The first source was the offender's MTC clinical and criminal archival records. The second comprised four record sources that were accessed to obtain comprehensive follow-up data. In this study, researchers coded these records both on modern empirically-derived, mechanical actuarials that have been developed since 1997 for predicting sexual recidivism, and on a new experimental measure. Two coding teams were created. In general Team A was responsible for (a) purifying, redacting, and scanning detailed copies of offenders' files, (b) classifying all BO sample using both the MTC typologies and the DSM-IV Conduct Disorder and Antisocial Personality Disorder categories, and (c) classifying a subset of the BT sample using the DSM-IV Conduct Disorder and Antisocial Personality Disorder categories. Team B was responsible for coding all actuarials and the Psychopathy Checklist-Revised on all offenders in the study, and for classifying all BT sample using the DSM-IV Conduct Disorder and Antisocial Personality Disorder categories.