Although their problem is often as disabling as in chronic schizophrenia, most cases of obsessive-compulsive disorder have become eminently treatable by the behavioural approach of live exposure with response prevention. Treatment takes from 1 to 6 months depending on the severity of the problem, and may need an overall mean therapist time of +/- 8 hours time per patient. Most psychiatrists can learn to apply the treatment quite quickly, and most patients can be treated on an outpatient basis. About 25% of patients refuse or do not complete behavioural treatment. Improvement has endured over the 5-year follow-ups available. Occasional cases need brief booster period during followup. In exposure treatment the sufferer is persuaded to come into prolonged contact with discomfiting cues that bring on the rituals, without ritualising, so that the ensuing anxiety and urge to ritualise can subside to the point of habituation. The contact should be for at least an hour daily, and should gradually involve all ritual-evoking cues. The patient should record all exposure tasks done in a daily self-exposure diary. The therapist does not need to do the exposure with the patient, his role being to educate the patient in what to do and to monitor and praise progress. Therapist-accompanied exposure is largely redundant. Where family members are involved in the rituals they need to be coopted, with the patient's agreement, as exposure cotherapists and taught in role rehearsal with the patient to withhold requests for reassurance. Antidepressant drugs are a useful adjuvant to exposure therapy when the patient's obsessive-compulsive problem is complicated by dysphoria.