Risperidone, an atypical neuroleptic, has been proposed for augmentation strategies in resistant obsessive-compulsive disorder (OCD). We report the results of an open-label trial on the use of the combination of serotonin reuptake inhibitors (SRIs) with risperidone in 20 refractory OCD outpatients. All patients had been suffering from OCD, according to DSM-IV criteria, for at least 2 years and had various comorbid disorders. All had been treated with a SRI at adequate dosages for at least 6 months, but had failed to respond. Therefore, risperidone was added and the dosage titrated up to the mean dose of 3 mg/day over 8 weeks. After 2 months of this regimen, all patients had shown a reduction in obsessive-compulsive symptoms, as assessed by the decrease in the Yale-Brown Obsessive-Compulsive Scale (Y-BOCS) total score, particularly those with a lifetime comorbidity with bipolar disorder; only three patients reported mild sedation and postural hypotension, two mild extrapyramidal side-effects (tremors and akatysia) and two an increased appetite. All these effects were well tolerated and no patient halted the treatment. The addition of risperidone would appear to be a useful strategy for augmenting SRI effectiveness in refractory OCD patients.