Background Klinefelter's syndrome is a sex chromosome abnormality affecting approximately 1 in 1000 men. There have been suggestions that it is associated with a higher than average prevalence of sexual offending but to what extent does research evidence support this assertion? Aims This study aimed to conduct a systematic review of published research to establish the prevalence of sexual offending in men with Klinefelter's syndrome. Method The databases MEDLINE, PsycINFO and EMBASE were searched from inception until 31 December 2016 by using a range of terms for Klinefelter's syndrome and for sexual offending. All selected papers were examined for quality by using the Strengthening the Reporting of Observational Studies in Epidemiology checklist. Results We identified 53 relevant papers of which 10 met our inclusion criteria. All but one were prevalence studies conducted in a prison or hospital setting. The one, Danish, register‐based cohort study did suggest an increased risk of sex offending among Klinefelter men, probably established before the diagnosis was made and, therefore, any hormone replacement instituted. Conclusion There is insufficient evidence to date to support concerns about exceptional risk of sex offending among men with Klinefelter's syndrome. Rather, it is arguable that there is a research gap in understanding how the experience of and treatment for their condition may affect them. Copyright © 2017 John Wiley & Sons, Ltd.