Relationships between Cloninger's temperament and character dimensions and plasma sex hormone levels and biogenic amine turnover were studied in male prison inmates convicted of rape (n=61) or child molestation (n=24) and normal male controls (n=25). The participants completed the Temperament and Character Inventory (TCI), which includes the temperament dimensions Novelty Seeking, Harm Avoidance, Reward Dependence and Persistence as well as the character dimensions Self-Directedness, Cooperativeness and Self-Transcendence. Plasma levels of testosterone, dihydrotestosterone, sex hormone binding globulin, luteinizing hormone (LH) and follicle-stimulating hormone were estimated in plasma samples and 5-hydroxyindoleacetic acid (5-HIAA), homovanillic acid (HVA), and 3-methoxy-4-hydroxyphenylglycol (MHPG) in urine samples. Both sex offender groups had higher Novelty, Seeking and lower Reward Dependence, Self-Directedness and Cooperativeness scores compared with the controls. Plasma levels of testosterone and dihydrotestosterone were significantly higher in rapists than in controls. Novelty Seeking scores were positively correlated with LH levels in rapists, and with testosterone levels in child molesters. Harm Avoidance scores were negatively correlated with 5-HIAA levels in rapists and with HVA levels in child molesters. In rapists, the calculated free androgen index showed a negative correlation with 5-HIAA. For the sex offender sample as a whole, the subgroup with high testosterone levels had higher Harm Avoidance scores, the subgroup with low HVA levels had lower Cooperativeness scores, and the subgroups with high 5HIAA or MHPG levels had lower Persistence scores. The results indicate that Novelty Seeking behavior in the group of rapists is associated with a hyperactive hypothalamic-pituitry-gonadal axis. In addition, low serotonin turnover and low dopamine turnover seem to be associated with a passive-avoidant behavioral style in rapists and child molesters, respectively.