Findings from numerous outcome studies have suggested that people with traumatic brain injuries (TBI) experience relationship difficulties and changes in sexuality. However, there have been few investigations of these problems. This paper reports the results of a study of sexuality following TBI, which aimed to identify changes in sexual behaviour, affect, self-esteem, and relationship quality, and their inter-relationships. Two hundred and eight participants with moderate-to-severe TBI (69% males) completed a questionnaire 1-5 years post-injury. Their responses were compared with those of 150 controls, matched for age, gender, and education. Of TBI participants 36-54% reported: (1) A decrease in the importance of sexuality, opportunities, and frequency of engaging in sexual activities; (2) reduced sex drive; (3) a decline in their ability to give their partner sexual satisfaction and to engage in sexual intercourse; and (4) decreased enjoyment of sexual activity and ability to stay aroused and to climax. The frequencies of such negative changes were significantly higher than those reported by controls and far outweighed the frequency of increases on these dimensions. A significant proportion of TBI participants also reported decreased self-confidence, sex appeal, higher levels of depression, and decreased communication levels and relationship quality with their sexual partner. Factors associated with sexual problems in the TBI group are explored and implications of all findings discussed.