The first breakthrough in the treatment of obsessive-compulsive disorder (OCD) came in 1967, when Fernandez and Lopez-Ibor reported on the efficacy of clomipramine (CMI) in the treatment of 16 patients with OCD (Fernandez and Lopez-Ibor, 1967). However, controlled studies with CMI were not published until 1980 (Montgomery, 1980; Thoren et al, 1980), and only in the last 5 years have large well-controlled studies been published (Clomipramine Collaborative Study, 1991). Several studies demonstrated that among the tricyclics (TCA), only CMI is effective in OCD, while effective antidepressants with a noradrenergic profile, such as desipramine (DMI), appear to be totally ineffective (Zohar and Insel, 1987; Goodman et al, 1990; Leonard et al, 1989). This selective response to TCA with a serotonergic profile led to the formulation of the serotonergic hypothesis of OCD and to the development and use of other serotonergic agents in the treatment of this disorder. Several drugs, possessing a serotonergic profile are currently being studied worldwide, among them CMI, fluoxetine, fluvoxamine, sertraline, paroxetine and citalopram. Currently, as the knowledge regarding the pharmacological approach to OCD is only beginning to accumulate, very little is known regarding treatment duration in OCD. In this review we shall attempt to examine the existing data regarding treatment duration in OCD.