Background: As cancer drug prices rise and insurance plans shift toward greater cost sharing, studies link patients’ high out-of-pocket (OOP) costs to non-adherence and early discontinuation of treatment. Meanwhile, few oncologists routinely discuss OOP costs with their patients. Using qualitative methods, we explored barriers and facilitators of cost transparency (i.e., disclosure of financial risks of cancer treatment). Methods: We performed semi-structured interviews with cancer patients (n = 22) and providers (n = 19) at an academic medical center and three affiliated community practices between August, 2015 and May, 2016. Two analysts coded the transcribed interview data using textual thematic methods, and hypotheses were generated employing grounded theory method. Results: We grouped themes that emerged into three major domains: 1) barriers, 2) facilitators, and 3) patient preferences. Patients and providers both expressed a strong aversion to making tradeoffs between financial and physical health outcomes. While patients feared being “profiled” based on their ability to pay, providers feared that cost transparency might threaten the doctor-patient relationship by exposing personal or institutional financial conflicts of interest. Pragmatic barriers included time constraints and difficulty in providing accurate cost estimates. Important facilitators were strong doctor-patient relationships and availability of support staff with financial expertise. We detected substantial heterogeneity in patient preferences. While some patients wanted to discuss costs with their provider, others feared “distracting” providers from their primary roles as health advocates. Conclusions: With implementation of OOP cost transparency, oncology practices will need to consider patient/provider aversion to financial/health tradeoffs, patients’ sensitivity to socioeconomic “profiling,” provider- and practice-level financial incentives, time constraints, accuracy of cost estimates, and variability in patient preferences. Meanwhile, strong provider-patient relationships and availability of support staff will facilitate OOP cost transparency.