Healthcare-based food assistance programs have the potential to improve patients' food security, but are underutilized. We conducted a qualitative study of user and staff perceptions of an on-site mobile market at a federally-qualified health center (FQHC). Five themes were identified: 1) financial need drives the decision to use the market, 2) people attend specifically to receive healthy food, 3) users feel a connection to the FQHC, which increases participation, 4) social networks increase usage of the program, and 5) long lines, inclement weather, inaccessibility, and inconsistent marketing and communication are attendance barriers. Findings should inform implementation of future healthcare-based food assistance programs.