Objectives: In this study, we explored determinants of "researcher-observed" patient-initiated antiretroviral therapy (ART) repackaging practices among people living with HIV (PLHIV) in Northern Tanzania. Methods: We used a quasi-experimental design to describe the prevalence of ART self- repackaging; we conducted face-to-face surveys to determine factors associated with ART self- repackaging practices. Data collection sites included the Kilimanjaro Christian Medical Centre and the Mawenzi Referral Hospital. We used study-specific numerical identifiers assigned to ARTs packaging to determine self-repackaging behavior. Self-repackaging was defined as a binary variable where participants who discarded antiretroviral drugs packaging in at least 2 clinic visits were classified as self- repackagers. We used multivariable logistic regression to assess the determinants of patient-initiated repackaging practices. Results: Among 590 study participants, 57.6% self-repackaged based on researcher observation and 55.6% self-repackaged based on patient report. Researcher-observed self- repackaging was associated with gender (AOR = 1.590; 95% CI: 1.011, 2.502), employment status (AOR = 0.475: 95% CI; 0.239, 0.942), and study site (AOR = 0.218; 95% CI: 0.134, 0.355). Conclusions: A substantial proportion of patients self-repackage their ARTs for various reasons. Health system interventions should focus on addressing the attributes of repackaging among men and unemployed patients.