BACKGROUND: Despite the increased use and acceptance of complementary and alternative medicine (CAM) practices and practitioners by patients and health care providers, there is relatively little information available concerning the reasons for use or its effect on patient health status and well-being. METHODS: We conducted a survey of 542 patients attending 16 family practice clinics that belong to a community-based research network in San Diego, California, to determine patients' reasons for using CAM therapies in conjunction with a visit to a family physician and the impact of these therapies on their health and well-being. RESULTS: Approximately 21% of the patients reported using one or more forms of CAM therapy in conjunction with the most important health problem underlying their visit to the physician. The most common forms of therapy were visiting chiropractors (34.5%) of CAM users), herbal remedies and supplements (26.7%), and massage therapy (17.2%). Recommendations from friends or coworkers, a desire to avoid the side effects of conventional treatments, or failure of conventional treatments to cure a problem were the most frequently cited reasons for using these therapies. Use of practitioner-based therapies was significantly and independently associated with poor perceived health status, poor emotional functioning, and a musculoskeletal disorder, usually low back pain. Use of self-care-based therapies was associated with high education and poor perceived general health compared with a year ago. Use of traditional folk remedies was associated with Hispanic ethnicity. CONCLUSIONS: Sociodemographic characteristics and clinical conditions that predict use of CAM therapies by primary care patients in conjunction with a current health problem vary with the type of therapy used.