Background: Survival outcomes for older patients with aggressive non-Hodgkin’s lymphoma (NHL) are disproportionally inferior to those of younger patients. While differences in tumor biology may play a role, older patients are often frail with comorbidities, polypharmacy, and use potentially inappropriate medications (PIM). Methods: Using Cox proportional hazard and logistic regression models, we retrospectively analyzed all aggressive NHL patients age 60 and older diagnosed and treated at our institution from 2009-2014 to examine the effect of polypharmacy and PIM use on progression-free survival (PFS), overall survival (OS), and treatment-related toxicities. Results: We included 141 patients with evaluable data after excluding patients with incomplete record. The median age was 71 years. At the time of diagnosis, 44% of patients used more than 4 medications and 47% used at least one PIM. During first-line treatment, only 43% of patients received chemotherapy of adequate relative dose intensity (>85% scheduled dose), and 63% experienced grade 3 or greater toxicities. Age, International Prognostic Index, and PIM use correlated with each other. Number of medications (p = 0.005) and PIM use (p < 0.001) were associated with shortened PFS by log-rank test, and PIM use remained a strong independent predictor of PFS in multivariable analysis (HR 1.84, p = 0.005). Number of medications (p = 0.003) and PIM use (p = 0.009) were also associated with shortened OS by log-rank test, although only albumin level predicted OS in multivariable analysis. Most importantly, PIM use was strongly associated with grade 3 or greater toxicities in multivariable analysis (OR 7.4, p = 0.001). Conclusions: We report here for the first time adverse impacts of polypharmacy and PIM use in older patients with aggressive lymphoma. We suggest that drug-drug interactions may significantly impair the delivery of adequate chemotherapy dosage and increase toxicities thus resulting in inferior survival outcome. Our findings support the use of evidence-based geriatric and palliative care principles to guide meticulous medication management to eliminate outcome disparity in older lymphoma patients.