Background: Homelessness happens when people or household are unable to acquire and/or maintain housing they can afford. Approximately 17% of homeless individuals are also chronically ill. Studies have often not objectively measured medication non- adherence among the homeless population, probably due to lack of consistent pharmacy records. This study proposed to objectively estimate medication non-adherence to chronic medications among the homeless population in Salt Lake City, Utah. Methods: A retrospective study design was used based on the pharmacy records from the Fourth Street Pharmacy based on four classes of chronic medications - asthma, diabetes, statins, and psychiatric medications. Data was collected between November 1, 2010 and February 28, 2011 on the variables: date of original prescription, number of refills on the original prescription, date of 1st, 2nd, 3rd, and 4th fills, age, gender, and race. Primary non-adherence and medication refill non-adherence based on Continuous Measure of Medication Gaps were calculated. Results: The medication refill non-adherence rate was 38.8% with asthma medications, 38.5% with diabetic medications, 27.2% with statins, and 47.1% with psychiatric medications. The primary non-adherence rate varied from zero percent to 20%. Conclusion: The study concluded that this population has comparable non-adherence rates with asthma, diabetes, cholesterol lowering, and certain psychiatric medications than the general population.   Type: Original Research