A progressive exploration of the role of personality in understanding offending in a child molester sample was undertaken. A particular focus was the extent to which the construct of personality could be used to reduce or account for some of the heterogeneity reported in this population. The studies used a sample of 110 participants in the Kia Marama treatment programme for sexual offenders against children. In the first of four studies these subjects were divided into four subgroups using cluster analysis of their scores on the Millon Clinical Multiaxial Inventory (MCMI) personality scales. The clusters resembled clusters found in other offender populations. A second study showed that while the four clusters were very similar on a range of demographic and background factors, they differed on a range of psychometric tests commonly used to assess child molesters. They were also found to respond differently to treatment. A third study investigated the possibility that the four clusters differed on factors that were directly related to their offending. The clusters were found not to differ in terms of their selection of victims, their relationship to victims, the extent and duration of their offending history, their convictions for sexual and other offences, their risk for future offending, or their actual re-offending rates following release after treatment. A fourth study further investigated the differences among the clusters regarding offending by analysing accounts of sexual offending behaviour against children held on police files. The clusters did not differ significantly on the measures used. A clinical profile is offered for each cluster. The clinical implications for the results are discussed with respect to risk, needs, and responsivity. Further theoretical implications are discussed together with a consideration of the contribution that personality makes to an understanding of sexual offending against children. The studies did not establish a link between personality and the actual offending behaviour of child molesters.