Many women use complementary and alternative medicine (CAM) to maintain or improve their health. We describe CAM use among the first 1,000 participants enrolled in the Pathways Study, an ongoing prospective cohort study of women diagnosed with breast cancer (BC). Participants, identified by rapid case ascertainment in Kaiser Permanente Northern California, are women > or = 21 years diagnosed with first invasive BC. Comprehensive baseline data are collected on CAM use through in-person interviews. Study participants include 70.9% non-Hispanic whites, 10.2% Hispanics, 9.0% Asians, 6.5% African-Americans, and 3.4% others. Most women (82.2%) were diagnosed with AJCC stage I/II BC at average (+/-SD) age 59.5 (+/-12.0) years and reported prior use of at least one form of CAM (96.5% of participants). In the 5 years before diagnosis, CAM therapies used at least weekly by >20% of women included green tea, glucosamine, omega-3 fatty acids, prayer and religion. CAM use was high (86.1% of participants) in the period immediately following diagnosis; 47.5% used botanical supplements, 47.2% used other natural products, 28.8% used special diets, 64.2% used mind-body healing, and 26.5% used body/energy/other treatments. In multivariable analyses, frequent use of each CAM modality before and after diagnosis was associated with use of other CAM modalities and other health behaviors (i.e., high fruit/vegetable intake, lower BMI). CAM use before and after BC diagnosis is common in this diverse group of women. Our results emphasize the need for clinicians to discuss CAM use with all BC patients.