This book is part of the World Psychiatric Association (WPA) series onEvidence and Experience in Psychiatry. Two years ago the WPA undertook to produce a review of areas of psychiatry in which there have been significant advances of knowledge, with the view that bringing together worldwide experts to review the current research evidence would result in further improvements in the provision of care. Obsessive—compulsive disorder (OCD) is one of the chosen areas. Over the past 20 years there has been a burgeoning interest in OCD, resulting from the recognition that it is not the extremely rare disorder it was once thought to be. Indeed, it has a worldwide prevalence of about 2% in the adult population, making it the fourth most common psychiatric disorder.

The book consists of six review chapters, written by international experts in OCD. Each review is followed by commentaries written by other experts in the field. A strength of these commentaries is that the authors often add to the reviews by describing further research or current practice in their own countries. This enables the reader to gain a truly worldwide perspective on some of the issues.

The first chapter, on diagnosis, summarises important aspects such as demographic features, classification and a typical course of the disorder and outlines the various assessment tools that are available. The following two chapters, on treatment, provide compelling evidence for the efficacy of both the selective serotonin reuptake inhibitors (SSRIs) and cognitive—behavioural therapy involving exposure and response prevention (E/RP). We are reminded that the challenge is both to ensure the wider provision of these effective treatments and also to remain aware of newer techniques under evaluation (such as the integrating of greater cognitive components for those patients reluctant to participate in E/RP or who have predominantly obsessional ruminations).

The chapter on the impact of OCD in children and adolescents is a very useful inclusion. Findings from retrospective studies have shown that 30-50% of adult patients with OCD had the onset of their symptoms during childhood or adolescence. Although the long-term outcome of childhood-onset OCD remains uncertain, there is increasing evidence that treatments similar to those used with adult patients may substantially help children to resume a normal developmental trajectory.

A chapter on the economics of OCD really only draws our attention to the paucity of work in this area. However, in our current climate of scarce resources, it reminds clinicians that there is already clear evidence for the cost-effectiveness of current therapeutic interventions for OCD, given the huge emotional and financial burden that the disorder places on society.

It is Hollander & Rosen's review of obsessive—compulsive spectrum disorders (OCSDs) that generates the most varied discussion. They construe OCSDs on a compulsive—impulsive dimension. Obsessive—compulsive disorder is therefore linked with a whole range of other disorders, such as pathological gambling, disorders where there is an exaggerated preoccupation with appearance, weight or bodily sensations, and neurological disorders with repetitive behaviours (e.g. Tourette syndrome and Syndenham's chorea). The authors propose that further confirmation for links with these disorders is their preferential response to SSRIs and behavioural therapy. On the whole, the commentators agree that there is value in the notion of a spectrum of disorders but there is a good deal of argument about the extent of disorders included. For example, with regard to the hypothesis of the preferential response to SSRIs, some reviewers point out that not all the disorders included respond to SSRIs in the same way and that, using this rubric, additional disorders such as anxiety and depression, could be included, which do respond favourably.

In my opinion, the editors have succeeded in putting together a book that reviews the current state of thinking in OCD. Each chapter review is concise and well-written, summarising current research findings and clinical practice and pinpointing areas for future research. The only problem with books of this nature is that they quite quickly become out of date but I would recommend this text as an excellent starting point for any health professional or policy-maker interested in finding out more about this disorder.