This article examines the psychometric properties of an adaptation of Levenson’s Locus of Control (LoC) measure that is used by the English and Welsh Prison Service as part of the psychometric assessment battery for sexual offenders participating in the Sex Offender Treatment Programme (SOTP). Reliability and validity analyses were conducted on a sample of 2,497 sexual offenders who had completed SOTP. Internal consistency, convergent validity, and relationship to socially desirable responding were investigated. Construct validity was assessed via exploratory factor analysis (EFA) and confirmatory factor analysis (CFA). Test-retest reliability data were collected from an additional sample of 26 sexual offenders. The scale was found to have excellent internal consistency, good test-retest reliability, and weak to moderate convergent validity with measures of self-esteem, attachment styles, emotional loneliness, and social problem solving. There was a moderate correlation between the scale and socially desirable responding. EFA and CFA suggested that a four-factor solution provided an acceptable fit to the data, with the factors relating to constructs of chance, problem solving, powerful others, and internal control. The findings of the present study suggest that the adapted LoC Scale is a useful tool for assessing sexual offenders’ locus of control.