AimThe aim of the study was to apply an intervention to the area of sexual knowledge in order to determine if capacity to make sexuality-related decisions could be improved.MethodThe study adopted a single subject design using multiple baseline method with four adults with a moderate intellectual disability. The intervention consisted of individually tailored sex education adapted from Living Your Life (Bustard 2003). Treatment was offered to each participant twice weekly for a 10-week period on a one-to-one basis. The Sexual Consent and Education Assessment (SCEA, Kennedy 1993) was used for measurement purposes. The SCEA K-Scale (knowledge) and the S-Scale (safety practices) were administered weekly throughout the baseline, treatment and post-treatment phases of the study. Staff concerns were also assessed using the SCEA Inappropriate Sexual Behaviour Scale.ResultsAll four participants improved their decision-making capacity in all targeted areas as measured by improvements in K-Scale and S-Scale scores. Staff concerns were not increased as indicated by results on the Inappropriate Sexual Behaviour Scale. Six-month follow-up data for three of the participants showed maintenance of scores on the S-Scale and some decay in scores on the K-Scale from post-intervention performance.ConclusionThe results demonstrate that tailored sexuality education can improve capacity to make sexuality-related decisions.