We conducted a hospital based case-control study of 245 cases of thyroid cancer (62 males and 183 females) and 411 controls in three areas of Northern Italy. Subjects with thyroid cancer more often had a history of benign thyroid nodules (18 cases versus 0 controls, lower 95% confidence limit = 7.84), goitre (RR = 5.61, 95% confidence interval (CI): 2.13-14.77) and residence in endemic goitre areas (RR for residence longer than 20 years = 2.29, 95% CI: 1.23-4.29). Heavy (greater than 1000 rads) irradiation of the neck was reported only by seven cases (lower 95% confidence limit: 2.45). Among 31 food items considered, a few showed direct association, including starchy foods and various sources of animal fats or proteins, whereas frequent consumption of other foods, including major sources of dietary iodine (such as fish, green vegetables and fruit) gave significant protection. When analysis was restricted to various subgroups of patients (ie, different histological types, sexes and major groups of hospital controls), it yielded similar results.