BACKGROUND: Little is known about the association between patient-oncologist discussion of cancer treatment out-of-pocket (OOP) cost and medication adherence, a critical component of quality cancer care. METHODS: We surveyed insured adults receiving anticancer therapy. Patients were asked if they had discussed OOP cost with their oncologist. Medication nonadherence was defined as skipping doses or taking less medication than prescribed to make prescriptions last longer, or not filling prescriptions because of cost. Multivariable analysis assessed the association between nonadherence and cost discussions. RESULTS: Among 300 respondents (86% response), 16% (n = 49) reported high or overwhelming financial distress. Nineteen percent (n = 56) reported talking to their oncologist about cost. Twenty-seven percent (n = 77) reported medication nonadherence. To make a prescription last longer, 14% (n = 42) skipped medication doses, and 11% (n = 33) took less medication than prescribed; 22% (n = 66) did not fill a prescription because of cost. Five percent (n = 14) reported chemotherapy nonadherence. To make a prescription last longer, 1% (n = 3) skipped chemotherapy doses, and 2% (n = 5) took less chemotherapy; 3% (n = 10) did not fill a chemotherapy prescription because of cost. In adjusted analyses, cost discussion (odds ratio [OR] = 2.58; 95% CI, 1.14 to 5.85; P = .02), financial distress (OR = 1.64, 95% CI, 1.38 to 1.96; P < .001) and higher financial burden than expected (OR = 2.89; 95% CI, 1.41 to 5.89; P < .01) were associated with increased odds of nonadherence. CONCLUSION: Patient-oncologist cost communication and financial distress were associated with medication nonadherence, suggesting that cost discussions are important for patients forced to make cost-related behavior alterations. Future research should examine the timing, content, and quality of cost-discussions.