This study was carried out to examine the factors that predicting the use of complementary and alternative medicine (CAM) among cancer patients in Tehran, Iran. Predicting factors included were patients' demographic characteristics, type of cancer, the knowledge of diagnosis, time since diagnosis, satisfaction with their care physician, fear of recurrence and measures of anxiety, depression and global quality of life. In total, 625 cancer patients were studied, and 35% (n=219) reported that they used or were using CAM. The most commonly used CAM was prayer and spiritual healing (n=178, 75.7% of responses). The results of logistic regression analysis indicated that the use of CAM among cancer patients was associated with the fear of cancer recurrence (OR=2.03, 95% CI=1.45-2.85, P<0.0001) and dissatisfaction with their care physician (OR=1.98, 95% CI=1.36-2.89, P<0.0001). The results indicate that apart from the prayer and spiritual healing, the use of the other common methods of CAM among Iranian cancer patients is unpopular. However, the findings suggest that the use of CAM is more common among cancer patients who suffer from fears, uncertainties and dissatisfaction, and these might be a marker of greater psychological distress in users as compared with non-users.