Purpose: The study was done to define complementary and alternative medicine (CAM) use among primary brain tumor patients and factors influencing use. Methods: The study was conducted with convenience sampling in 5 neuro-oncology centers in Seoul and Gyeonggi Province. Data were collected using a 25-item questionnaire developed by the researchers. Results: Of 250 patients approached, 231 (92.4%) agreed to participate. Overall, 26.8% of the respondents used CAM and the average cost for CAM use was 300,000 KRW. More than 72% of CAM users did not disclose CAM use to their health care professionals. The most frequently used therapy was natural products including mushrooms. Logistic regression analysis revealed that an education level of university or higher (OR=2.92, 95% CI=1.56-5.44, p=.001), unemployment (OR=1.99, 95% CI=1.04-3.80, p=.037), and WHO grade III & IV tumors (OR=2.18, 95% CI=1.07-4.72, p=.048) were significant factors influencing CAM use. Conclusion: Three out of ten brain tumor patients spend substantial sum of money for CAM. In these situations, health care professionals should be aware of this phenomenon and provide adequate information and consultation to the patients.