Objectives: The purpose of this study was to determine patient characteristics and other factors associated with discontinuation of complementary and alternative medicine (CAM) among cancer patients in Korea. Methods: A national, multicenter, cross-sectional survey of cancer patients was performed in which 674 of 2,661 patients were analyzed for their use of CAM after cancer diagnosis. Multiple logistic regression was used to identify the factors related to CAM discontinuation. Results: Among the surveyed cancer patients, 25.3% (674 of 2,661) had used CAM, whereas 38.3% (258 of 674) of those with CAM experience had discontinued CAM therapy. The most frequently used form of CAM was herbs (43.5%). The major reasons for the discontinuation of CAM included absence of effects (23.9%), financial burden (22.9%), and physician opposition (13.7%). Other factors associated with the discontinuation of CAM included metastatic cancer (OR = 2.06), a long duration of cancer treatment (OR = 3.34), dissatisfaction (OR = 4.34), and side effects (OR = 4.23) of CAM therapy. Conclusions: For cancer patients to correctly employ CAM therapy, increase their satisfaction, and reduce their side effects, efforts should be made to analyze the cost effectiveness of CAM, and valid information must be provided to physicians and cancer patients.