Background: CBD is derived from cannabis and has minimal psychoactive effect. We sought to evaluate factors associated with CBD use among patients who received cancer treatment and elucidate the reasons for use, and perceived benefits of CBD. Methods: An anonymous online or phone survey was administered to patients treated for cancer between 3/2021-8/2021 at a comprehensive cancer center; only patients residing in states where cannabis is legal were contacted. Surveys were completed 8/2021-4/2022. Patient-reported use of cannabis and CBD products was assessed, as well as beliefs and perceptions regarding CBD. Unadjusted and weighted multivariable logistic regression (MVA) was used to assess factors associated with CBD use after diagnosis. Results: Among 1258 patients (35% response rate), 41% knew either “a lot” or “some” about CBD, 44% knew “a little”, 15% knew nothing or were unsure. Of those who had heard about CBD, 69% felt there were no risks of taking CBD. 370 patients (29%) both knew of CBD and endorsed cannabis use after diagnosis; 61% of that group, 226 (18% of all surveyed) specifically reported CBD use. Those who reported CBD use were 54% women, 83% white, and 88% non-Hispanic, with a median age of 63 (IQR 52-71). 75% of CBD users had used any cannabis product at least once prior to diagnosis and 40% of CBD users had used cannabis in the year prior to diagnosis. Among the 150 patients who used CBD during treatment, 54% used it several times a week or more; 49% used CBD after treatment completion. Among CBD users, common reasons for CBD use were pain (56%, n = 125), sleep (48%, n = 107), mood (36%, n = 80), or neuropathy (18%, n = 40). Symptom benefit from CBD (improved “somewhat” or “quite a bit”) was reported for pain (71%), sleep (71%), mood (74%), and neuropathy (60%). Only 1% reported worsening of non-target symptoms or side effects with CBD; 3% felt it worsened neuropathy. Overall, 47% either stopped using CBD or used it less than they would prefer due to no benefit (30%), high cost (25%), or lack of insurance coverage (21%). On weighted MVA, patients who were ≤45 (OR 1.16, 95%CI 1.06-1.26, p < 0.01) or 46-64 (OR 1.10, 95%CI 1.04-1.27, p < 0.01) were more likely to use CBD after diagnosis than those ≥65. Prior cannabis use, compared to no prior cannabis use, was associated with CBD use after diagnosis (OR 1.13, 95%CI 1.08-1.19, p < 0.01). Compared to patients with lung cancer, patients with gastrointestinal cancer were more likely to use CBD after diagnosis (OR 1.11, 95%CI 1.00-1.22, p = 0.04). Conclusions: Fewer than half of surveyed patients treated for cancer had good knowledge of CBD, however most felt it was safe to use without any risks. Almost one in five surveyed had used CBD after diagnosis for a variety of symptoms. Patient-reported benefits were high and negative side effects were rare except for cost. Additional research is needed to help guide patient use of CBD given weak evidence of benefits.