Current serotonin reuptake inhibitor (SRI) treatments for obsessive-compulsive disorder (OCD) provide only partial benefit. A previous study suggested that inositol alone is efficacious in OCD. Ten DSM-IV OCD patients completed a study of 18 g inositol or placebo for 6 wk each in addition to ongoing SRI treatment in a double-blind randomized cross-over design. Weekly assessments included the Yale-Brown Obsessive-Compulsive Scale (YBOCS) and Hamilton Depression and Anxiety scales. No significant difference was found between the two treatment phases.