Researchers at Karolinska Institutet analyzed the incidences of mental illness and drug abuse in 93 convicted women and compared them with more than 20,000 randomly selected women in the general population and with about 13,000 women convicted of non-sexual crimes over the same period.

Between 1988 and 2000, 93 women and 8,500 men were convicted of sexual offenses in Sweden.

Niklas Langstrom of the Karolinska Institutet's Centre for Violence Prevention said 37 percent of the women convicted of sex offenses had undergone treatment at a psychiatric clinic during the period and 8 percent had been diagnosed as having a psychosis.

The study, published in the Archives of Sexual Behavior, found no difference in incidences of mental illness and drug abuse between these women and women who had committed other kinds of violent crime, Langstrom said.

However, incidences of psychosis were 16 times higher among the sex offenders than the control group, while drug abuse was 23 times higher.

Sexual offense is defined for this study as rape, non-consensual sex, sexual abuse and sexual molestation.