OBJECTIVES: Conventional typical-antipsychotics are less tolerated than newer atypical-antipsychotics. Concerns about using antipsychotic-combinations also exist. However, national studies of antipsychotic use at United States (US) ambulatory visits are limited. The study objectives were to determine national estimates and associated factors of antipsychotic (typical, atypical, and combination) use. METHODS: Retrospective analyses were conducted of the combined 8-year data (1996-2003) of office-based National Ambulatory Medical Care Survey (NAMCS) and outpatient National Hospital Ambulatory Medical Care Survey (NHAMCS). Mental-health disorder visits with ICD-9-CM diagnostic-codes (290-319, 331.0x) were classified into three mutually exclusive visit-groups: typical, atypical or combined-antipsychotic. Sample estimates were weighted and projected to the population with 95% confidence intervals. Multivariable logistic regression was used to determine significant factors associated with typical- versus atypical-antipsychotic mention at visits. RESULTS: About 47.7million visits or 0.83% (95%CI:0.73-0.93) of all adult visits had a mental-health disorder and an antipsychotic mention: atypical (30 million visits), typical (15.3 million visits), and combination (2.4 million visits). Major antipsychotics across visit-groups were: typical (haloperidol, thioridazine, fluphenazine); atypical (risperidone, olanzapine, quiteapine); and combination (haloperidol, risperidone, olanzapine). Compared with typical-, the likelihood of atypical-antipsychotic visits increased over time. More typical- and combination- versus atypical-antipsychotic visits (30% and 37%vs.7%) included medications to treat extrapyramidal side effects (EPS). In multivariable logistic-regression analysis, controlling for gender, schizophrenia-diagnosis, and behavioral-treatment; age greater than 40 versus 18-40 years (odds-ratio, OR,0.65,95%CI:0.49-0.85) and nonprivate insurance reimbursement-sources significantly decreased while comorbid depression (OR,1.9,95%CI:1.23-2.85), and bipolar-disorder (OR,2.0,95%CI:1.27-3.24), significantly increased the likelihood of atypical- relative to typical-antipsychotic mention at visits (p<0.05). CONCLUSIONS: Although combination-antipsychotic visits were low, 37% of these visits included medications to treat EPS. Atypical-antipsychotic use was more likely at visits by younger patients, with comorbid diagnoses (depression, bipolar-disorder), and private insurance reimbursement-source. This highlights important case-mix factors of antipsychotic use warranting attention in US ambulatory care to guide formulary-decisions.