BACKGROUND Many nightmare sufferers do not consult a health care professional. Though behavior and cognitive therapy can help, they have not been tested as a self-treatment method at home using a manual. METHOD One hundred and seventy adults with primary nightmares were randomised to four weeks' self-exposure or self-relaxation at home using manuals posted to them, or to a waiting-list as a control group for four weeks. Individuals recorded nightmare frequency and intensity in four-week diaries. RESULTS At one- and six-month follow-up, the self-rated nightmare frequency fell more significantly in exposure subjects than relaxation or waiting-list subjects. The self-exposure group had the most drop-outs but remained superior in an over-cautious intent-to-treat analysis. The individuals' partners confirmed the superiority of self-exposure to self-relaxation at one- and six-month follow-up. CONCLUSIONS Recurrent nightmare sufferers improved more with self-exposure manuals than with self-relaxation manuals or by being on a waiting-list. Self-exposure may be needed for longer than four weeks in order to reduce nightmare intensity as well as frequency. Despite a high drop-out rate, some sufferers of other conditions may benefit from self-treatment manuals.