OBJECTIVES: To investigate the cancer patients’ CAM disclosure to the health care provider. METHODS: The study was designed as a questionnaire based, cross sectional analysis. A prevalence based sample of 393 cancer patients admitted to the oncology ward at Penang General Hospital was hereby selected for the study. RESULTS: Of 393 patients, 184 (46.1%) were identified as CAM users and among them 126 (68.5%) were actively reported to use one or more types of CAM at the time of interview.  CAM disclosure rate was 43%, while only in 33.7% cases, patients been asked by their doctors on the CAM use. The most common reason of CAM non-disclosure was ‘not important for doctors to know about CAM’ 63 (34.2%). Among other reasons were, ‘doctors never asked about CAM’ 15(8.2%), ‘doctors have little knowledge about CAM’ 9(5.9%), ‘fear of CAM disapproval by the doctors’ 8(4.3%) and fear of termination of therapy by the doctors’ 6(3.3%). Among the demographic variables patients having a history of regular health checkups before cancer diagnosis were tend to discuss their CAM use with the doctors (r=0.16, p=0.02). Perceived severity of side effects due to conventional therapies was positively correlated (r=0.18, p=0.014) with CAM disclosure. Patients who received recommendations on CAM from friends and family members were tend not to disclose their CAM use (r= -0.17, p=0.02). However those received recommendations from their health care providers were more likely to disclose CAM use (r=0.3, p<0.001). Previous experiences of side effects due to CAM therapies was positively correlated (r=0.14, p=0.04) with CAM disclosure behavior. CONCLUSIONS: Understanding the underlying beliefs of patients’ reluctance to disclose CAM usage to healthcare providers is important especially when they are on active cancer treatment. A friendly non-judgmental discussion about CAM use by the physicians may improve patients’ CAM behavior towards CAM disclosure.