OBJECTIVES: To examine treatment and pharmaceutical utilization patterns for patients receiving risperidone, olanzapine or quetiapine in a VA system. METHODS: This study used electronic claims data (VISTA system) to identify subjects prescribed atypical antipsychotics between January 1, 1996 and June 30, 2001. Included subjects were prescribed at least one study medication and had at least two markers for any of the following mental health disorders: bipolar, depression, schizophrenia, schizoaffective disorder, dementia, or PTSD. Demographics, average dose by diagnosis, adherence to VA Guidelines, duration of therapy, concomitant medication use, and switching were analyzed descriptively. RESULTS: Of 7,658 total study patients, the following number of patients received at least 1 prescription for the following drugs: olanzapine (4363), risperidone (3878), quetiapine (1387). The proportion of subjects with a schizophrenia diagnosis receiving dose ranges consistent with VA published guidelines for olanzapine, risperidone, and quetiapine were 90, 75 and 41% respectively, but varied greatly by diagnosis. Mean duration of therapy for all diagnoses was 146, 149, and 114 days for olanzapine, risperidone and quetiapine respectively. Mean duration of therapy varied widely by diagnostic conditions (190, 202 & 171 days for schizoaffective disorder, 146, 131 & 121 days for PTSD all for olanzapine, risperidone and quetiapine respectively). Concomitant use of more than one atypical antipsychotic medication occurred in 17-25% of patients, and most commonly with quetiapine. Concomitant use of any other psychotropic medication was similar in subjects receiving risperidone, olanzapine, and quetiapine (85, 86, 85% respectively). Twenty two percent of patients switched atypical therapy at some point during the study period. Of patients who had received therapy for at least 10 weeks and switched atypical, the most common switching occurred from olanzapine to quetiapine (48%). CONCLUSIONS: Dosing and duration of therapy of atypical antipsychotics in the Cleveland VA varies widely between diagnostic conditions.