Background Much of the research on the prevalence of psychiatric disorders among sex offenders has been conducted in the USA or Europe. Less is known about it in other regions, particularly in Asia. Aims The objective of this study is to determine the prevalence of psychiatric disorders among sex offenders in Taiwan and their associations with offender characteristics and criminal history. Methods Participants were randomly selected from men serving sentences in Taiwan's prison for serious sex offenders. Consenting men were assessed using the structured clinical interviews for DSM-IV-TR Axis I and II disorders. Demographics and criminal history were also recorded. Results Over two-thirds of the 68 participants met criteria for one or more lifetime Axis I disorders, and nearly 60% met criteria for one or more Axis II disorder. The higher the number of Axis I and cluster B personality disorders, the higher was the total number of convictions. Conclusions Our study adds to the literature that suggests that psychiatric assessment is likely to have an important role in the management and treatment of sex offenders. The finding that multiple disorders are common in this group and associated with more convictions for sex offences suggests that failure to include psychiatric assessment in planning the management of sex offenders may increase the risk of recidivism.