Obsessive–compulsive disorder (OCD) has recently undergone a dramatic change in status. Once regarded as a rare example of the neuroses, it now occupies a central position in contemporary psychiatry. The reasons for this renaissance in interest are relatively easy to describe. Firstly, results from the National Institute of Mental Health Epidemiological Catchment Area (ECA) survey indicated that the lifetime prevalence of OCD was 2.5% (1 in 40 people) and the 6-month point prevalence was 1.5%, making it the fourth most common psychiatric disorder in the US (Myers et al, 1984; Robins et al, 1984; Karno et al, 1988). If these figures are applicable to the UK, there may be up to 1 million sufferers. Secondly, the therapeutic efficacy of the selective serotonin reuptake inhibitors (SSRIs) and consistent findings from a number of neuroimaging investigations have stimulated interest in understanding the biological substrates of OCD. Finally, the traditional behavioural account of OCD has been elaborated, with greater emphasis given to cognition and cognitive processes; this revised anatomy of obsessions has, predictably, stimulated the development of specific cognitive therapy strategies.