Public Release: 

Sex crimes more common in certain families

Karolinska Institutet

New research from Sweden's Karolinska Institutet in collaboration with Oxford University, UK, shows that close relatives of men convicted of sexual offences commit similar offences themselves more frequently than comparison subjects. This is due to genetic factors rather than shared family environment. The study includes all men convicted of sex crime in Sweden during 37 years.

"Importantly, this does not imply that sons or brothers of sex offenders inevitably become offenders too", says Niklas Langstrom, Professor of Psychiatric Epidemiology at Karolinska Institutet and the study's lead author. "But although sex crime convictions are relatively few overall, our study shows that the family risk increase is substantial. Preventive treatment for families at risk could possibly reduce the number of future victims."

The report is published in the International Journal of Epidemiology and based on anonymised data from the nationwide Swedish crime and multigeneration registers.The research included all 21,566 men convicted for sex offences in Sweden between 1973 and 2009, for example rape of an adult (6,131 offenders) and child molestation (4,465 offenders). The researchers looked at the share of sex crimes perpetrated by fathers and brothers of convicted male sex offenders and compared this to the proportion among comparison men from the general population with similar age and family relationships.

The results suggested familial clustering of sex offenders, about 2.5 percent of brothers or sons of convicted sex crime offenders are themselves convicted for sex crimes. The equivalent figure for men in the general population is about 0.5 percent. Using a well-established statistical calculation model, the researchers also analysed the importance of genetic and environmental factors for the risk of being convicted of sexual abuse.

"We found that sex crimes mainly depended on genetic factors and environmental factors that family members do not share with one another, corresponding to about 40 percent and 58 percent, respectively", says Niklas Langstrom. "Such factors could include emotional lability and aggression, pro-criminal thinking, deviant sexual preferences and preoccupation with sex."

Self-reported sexual victimization rates in Sweden are largely similar to those in other Western and central European nations, Canada and the USA. Other cross-national comparisons of police-reported offences should be done cautiously because of differences in legal definitions, methods of offence counting and recording, and low and varying reporting rates of sexual violence to the police.


The research was funded by the Swedish Prison and Probation Service R&D, the Swedish Research Council, the Wellcome Trust and the CIHR Banting fellowship program. Niklas Langstrom is also the national scientific advisor for the Swedish Prison and Probation Service.

Open access publication: 'Sexual offending runs in families: A 37-year nationwide study', Niklas Langstrom, Kelly M. Babchishin, Seena Fazel, Paul Lichtenstein & Thomas Frisell, International Journal of Epidemiology, online 9 April 2015.

Journal website:

Karolinska Institutet is one of the world's leading medical universities. Its vision is to significantly contribute to the improvement of human health. Karolinska Institutet accounts for over 40 percent of the medical academic research conducted in Sweden and offers the country's broadest range of education in medicine and health sciences. The Nobel Assembly at Karolinska Institutet selects the Nobel laureates in Physiology or Medicine. More about us on

Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.