Serotonin-reuptake inhibitors have come forth to become the mainstay of treatment in obsessive compulsive disorder (OCD), predominantly as a result of evidence from clinical psychopharmacological response studies. Comorbid psychiatric disorders frequent OCD patients, most often depression. Although selective serotonin reuptake inhibitors are effective in the treatment of both OCD and depressive disorder, all antidepressants are associated with treatment-emergent affective switch. We present a 48-year-old patient with OCD, on antidepressants, initially for OCD and later for depression as well. She switched to mania after 20 years of treatment, which responded to olanzapine and divalproex sodium.