PURPOSE: Despite increasing availability of biosimilar cancer treatments, little is known about oncologists' knowledge and concerns regarding biosimilar use in the United States. We surveyed medical oncologists to examine their knowledge, attitudes, and experience with biosimilars. METHODS: Oncologists recruited via the ASCO Research Survey Pool completed a 29-question survey in 2020 designed with input from clinical and health care system experts and literature review. RESULTS: Of the 269 respondents, most treated patients with biosimilars (n = 236, 88%) and reported that biosimilars were required at their institution (n = 168, 63%). Approximately half (n = 140, 52%) of oncologists correctly responded that biosimilars were not the same as generic medicines. Commonly reported barriers to use of biosimilars included concerns regarding a perceived lack of relevant research (n = 85, 33% reporting quite a bit/very much), the potential for extrapolation (n = 83, 33%), and efficacy limitations (n = 77, 30%). More oncologists from university hospitals (n = 36, 22%) than from community/private hospitals (n = 28, 38%) or private practices (n = 13, 38%) were concerned about biosimilar efficacy. A high proportion of oncologists reported that information on safety (n = 259, 99%) and efficacy (n = 255, 99%) is important when considering whether to use biosimilars. Less than half reported that their institution provided education about biosimilars (n = 108, 40%). CONCLUSION: In this sample of medical oncologists, knowledge about basic features of biosimilars was limited and access to information about biosimilars was insufficient. The present study determined that educational programs on biosimilars for oncologists are needed and identified priorities for such efforts.