The purpose of this study was to determine the frequency of body image and sexual problems in the first months after treatment among women diagnosed with breast cancer at age 50 or younger. Breast cancer treatment may have severe effects on the bodies of younger women. Surgical treatment may be disfiguring, chemotherapy may cause abrupt menopause, and hormone replacement is not recommended. A multi-ethnic population-based sample of 549 women aged 22-50 who were married or in a stable unmarried relationship were interviewed within seven months of diagnosis with in situ, local, or regional breast cancer. Body image and sexual problems were experienced by a substantial proportion of women in the early months after diagnosis. Half of the 546 women experienced two or more body image problems some of the time (33%), or at least one problem much of the time (17%). Among sexually active women, greater body image problems were associated with mastectomy and possible reconstruction, hair loss from chemotherapy, concern with weight gain or loss, poorer mental health, lower self-esteem, and partner's difficulty understanding one's feelings. Among the 360 sexually active women, half (52%) reported having a little problem in two or more areas of sexual functioning (24%), or a definite or serious problem in at least one area (28%). Greater sexual problems were associated with vaginal dryness, poorer mental health, being married, partner's difficulty understanding one's feelings, and more body image problems, and there were significant ethnic differences in reported severity. Difficulties related to sexuality and sexual functioning were common and occurred soon after surgical and adjuvant treatment. Addressing these problems is essential to improve the quality of life of young women with breast cancer.