Background: Many hypotheses have been proposed to address the relationship between sex offenders and neuropsychological functions. Method: The purpose of this study was to evaluate differences in executive functions between juvenile sex offenders and non-sex offenders with/without low IQ by using the Behavioural Assessment of the Dysexecutive Syndrome (BADS) and the Wechsler IQ Test. Results: The sex offenders with low IQ had significantly lower scores than the non-sex offenders with low IQ in switching attention, processing speed, working memory, and prospective memory. No differences between the sex offenders and the non-sex offenders without low IQ were found in all tests. Conclusion: These findings show that the neuropsychological characteristics of juvenile sex offenders are related to their IQ level, and suggest that juvenile sexual offending is related to the possibility of having developmental deficits. The combination of cognitive behavioural therapy and neurocognitive training for treatment is therefore important.