OBJECTIVES: This study examines the availability of and eligibility requirements for  pharmaceutical patient assistance programs (PAPs) for the most commonly prescribed medications in the United States. METHODS: RxAssist.org, an electronic database of PAPs, was utilized to collect information on the availability (brand and/or generic) and eligibility (citizenship, permanent residency, insurance, and income limits) for each of the “Top 200 drugs by dispensed prescriptions” for 2008. Pharmaceutical companies were contacted directly or their websites were searched when additional clarifications were needed. Chi-square analyses were used to assess for differences in eligibility requirements by drug availability (brand or generic). RESULTS: Of 136 unique chemical entities, 111 (81.6%) of these drugs were available in RxAsisst.org.  69 (62.2%) of the available drugs were brand only, 29 (26.1%) generic only and 13 (11.7%) had both brand/generic forms. There were differences found in PAP eligibility requirements for citizenship (p<0.001), permanent residency (p<0.001), and private insurance status (p<0.001) by drug availability (brand versus generic), but not for income limits (p= 0.051).  Some programs allow Medicare Part D patients to apply for PAP; however, each claim is evaluated on case-to-case basis. CONCLUSIONS: Both brand and generic drugs are widely available to low-income applications through PAPs, but results suggest that U.S. citizenship and permanent residency are more likely to be required by PAPs for brand versus generic drugs. PAPs also provide some options for the underinsured—those with either private insurance or Medicare Part D coverage.