Obsessive-compulsive disorder (OCD), classified as a severe mental illness by the National Advisory Mental Health Council, affects 2.1% of the population annually, as shown by the Epidemiological Catchment Area surveys. This study, using the human capital approach, estimated the direct and indirect costs of OCD. The total costs of OCD were estimated to be $8.4 billion in 1990, 5.7% of the estimated $147.8 billion cost of all mental illness, and 18.0% of the costs of all anxiety disorders, estimated to be $46.6 billion. The indirect costs of OCD, reflecting lost productivity of individuals suffering from or dying from the disorder, were estimated at $6.2 billion.