The glycemic index (GI) and glycemic load (GL) have been considered risk factors for breast cancer, butassociation studies of breast cancer risk using simple GI and GL might be affected by confounding effects of theoverall diet. A total of 357 cases and 357 age-matched controls were enrolled, and dietary intake was assessedusing a validated food frequency questionnaire (FFQ) with 103 food items. GI and GL dietary patterns werederived by reduced rank regression (RRR) method. The GI and GL pattern scores were positively associatedwith breast cancer risk among postmenopausal women [OR (95%CI): 3.31 (1.06-10.39), p for trend=0.031; 9.24(2.93-29.14), p for trend<0.001, respectively], while the GI pattern showed no statistically significant effects onbreast cancer risk, and the GL pattern was only marginally significant, among premenopausal women (p fortrend=0.043). The GI and GL pattern scores were positively associated with the risk of breast cancer in subgroupsdefined by hormone receptor status in postmenopausal women. The GI and GL patterns based on all food itemsconsumed were positively associated with breast cancer.