OBJECTIVE: To describe factors that are associated with variations in the prescribed average daily dose of ziprasidone for the treatment of schizophrenia. METHODS: We identified continuously enrolled patients with a diagnosis of schizophrenia (ICD-9 code 295.xx) between January 2001 and June 2003 from Maryland Medicaid. The average daily dose prescribed was defined as the total amount dispensed divided by the days of therapy. The effect of socio-demographic factors, recent hospitalization, psychiatric co-morbidities, and concurrent psychiatric medication on the average daily dose prescribed was estimated using ordinary least squares (OLS) regression. RESULTS: In the sample of 1,197 patients who met the inclusion criteria, the mean average dose prescribed was 92 mg per day (S.D.: 50 mg). Males were prescribed an 8 mg higher average daily dose as compared to females (p=0.007). African Americans were prescribed 9 mg less as compared to Caucasians (p=0.005). The average daily dose prescribed increased if the patient was concurrently treated with antidepressants by 8 mg (p=0.018), with antipsychotics by 16 mg (p<0.001), and with anticonvulsants by 12 mg (p=0.001). Patients who had a psychiatric hospitalization during the 30 days prior to initiation of therapy were prescribed average daily doses that were 8 mg higher, but this increase was not statistically significant (p=0.055). Patient age, the number of psychiatric co-morbidities, and concurrent treatment with antimanic and antianxiety medication were not found to statistically affect prescribing patterns. CONCLUSION: Schizophrenia patients' gender, race, and concurrent treatment medication significantly affect the decision makers prescribing patterns of ziprasidone in terms of the average daily dose.