BACKGROUND: Few studies have examined the use of immunoassay urine drug testing of cancer patients in palliative care clinics. OBJECTIVES: We examined the frequency of immunoassay urine drug test (UDT) abnormalities and the factors associated with aberrancy at a safety-net hospital palliative medicine clinic. METHODS: A retrospective review of the electronic medical records of consecutive eligible patients seen at the outpatient palliative medicine clinic in a resource-limited safety net hospital system was conducted between September 1, 2015 and December 31, 2020. We collected longitudinal data on patient demographics, UDT findings, and potential predictors of aberrant results. RESULTS: Of the 913 patients in the study, 500 (55%) underwent UDT testing, with 455 (50%) having the testing within the first three visits. Among those tested within the first three visits, 125 (27%) had aberrant UDT results; 44 (35%) of these 125 patients were positive for cocaine. In a multivariable regression model analysis of predictors for aberrant UDT within the first 3 visits, non-Hispanic White race (odds ratio [OR]=2.13; 95% confidence interval [CI]: 1.03-4.38; p=0.04), history of illicit drug use (OR=3.57; CI: 1.78-7.13; p< 0.001), and history of marijuana use (OR=7.05; CI: 3.85-12.91; p< 0.001) were independent predictors of an aberrant UDT finding. CONCLUSION: Despite limitations of immunoassay UDT, it was able to detect aberrant drug taking behaviors in a significant number of patients seen at a safety net hospital palliative care clinic, including cocaine use. These findings support universal UDT monitoring and utility of immunoassay-based UDT in resource limited settings.