PURPOSE: To report on the use of pharmaceutical patient assistance programs (PAPs) in the outpatient pharmacy at the largest tertiary cancer center in the United States. METHODS: We conducted a retrospective (July 1, 2006-Dec 31,2007) cross-sectional analysis of outpatient pharmacy, medical, and cancer registry records at the cancer center. The cancer center identified 104 medications available through PAPs. Study-eligible patients received at least one of these medications, either as a PAP case patient or as a PAP control non-user. Binary logit regression models predicted PAP use, and descriptive statistics compared PAP user and non-user medication fills. RESULTS: Of 25,552 cancer patients at who received an outpatient medication during the study period, 1,929 met study criteria (n=950 PAP users, 979 PAP non-users). In comparison to controls, PAP users were more likely to be uninsured (odds ratio (OR)=4.60, 95% confidence interval (CI): 2.118, 9.970), indigent (OR=16.95, 95% CI: 6.845, 41.960), and < 65 years old (OR=2.31, 95% CI: 1.517, 3.509). Of the most frequently dispensed medications to PAP users from PAPs (n=5,271), 88% (n=4,936) were for supportive care (e.g., nausea/vomiting). PAPs provided 35% (n=842) of the most common anticancer agents administered to PAP users (n=1,296), accounting for a monthly mean of $55,000 in pharmaceutical expenditures. CONCLUSIONS: In the cancer center's outpatient pharmacy, PAPs provided financial support for about a third of the most commonly used therapies, primarily for supportive care indications, for a small percentage of eligible cancer patients.