BACKGROUND Many breast cancer patients use some form of dietary supplement (DS) to complement their conventional cancer treatment, in the hope that they might lessen the side effects of treatment, improve quality of life, give a greater sense of control, and reduce stress. This pilot study assessed the level of DS usage by breast cancer patients undergoing conventional cancer treatment, and their concerns about the use of DS. METHOD A cross-sectional descriptive survey in three breast cancer centers in Hong Kong using face-to-face interviewing was performed. RESULTS Of 82 female Chinese breast cancer patients who completed the survey, 99% reported that they had been using DS since their cancer was diagnosed. The most frequently used DS were Chinese herbal medicines, and patients spent about US$258 on DS every month. The reason given for using DS was to enhance their recovery from cancer, but at the same time the patients had safety concerns. However, most patients did not feel able to discuss these concerns with health professionals. CONCLUSION The majority of the patients had some safety concerns, and said that they would welcome detailed and reliable information on DS. The lack of reliable information on the potential risks and benefits of using such supplements as an adjuvant to conventional treatment and the reluctance of patients to discuss their use of DS with health professionals is a major area of concern that warrants further attention.