To analyze the risk factors of thyroid cancer among Japanese women who generally consume much more iodine than Europeans, we conducted a hospital-based case-referent study at Aichi Cancer Center Hospital (ACCH) in Nagoya, Japan. Ninety-four female patients aged between 20-79 years with papillary or follicular carcinoma of the thyroid, and 22,666 female outpatients without cancer were used. Past history of benign thyroid mass or goiter (odds ratio: OR = 13.9) and hyperthyroidism (OR = 5.0) showed increased ORs of thyroid cancer. Thyroid cancer cases consumed coffee less frequently (OR = 0.5) and had had more experience of delivery than referents (> or = 3 times; OR = 2.5). Western style breakfast (OR = 0.5) also decreased the OR. For the multivariate analysis, past history of thyroid diseases (OR = 4.3) was positively associated with the risk of thyroid cancer and everyday coffee consumption (OR = 0.6) tended to decrease the risk. These results suggest that thyroid hormone-related factors may be involved in the risk of thyroid cancer in Japan, too. To clarify the risk involved in Japanese food, another comparative study including detailed information on iodine intake between countries and individuals is required.