Results from case-control and prospective studies suggest a moderate positive association between obesity and height and differentiated thyroid carcinoma (TC). Little is known on the relationship between other measures of adiposity and differentiated TC risk. Here, we present the results of a study on body size and risk of differentiated TC based on a large European prospective study (EPIC). During follow-up, 508 incident cases of differentiated TC were identified in women, and 58 in men. 78% of cases were papillary TC. Cox proportional hazard models were used to estimate hazard ratios (HRs). In women, differentiated TC risk was significantly associated with body mass index (BMI, kg/m2) (HR highest vs lowest quintile = 1.41, 95% CI: 1.03–1.94); height (HR = 1.61; 95% CI: 1.18–2.20); HR highest vs lowest tertile waist (HR = 1.34, 95% CI: 1.00–1.79) and waist-to-hip ratio (HR = 1.42, 95% CI: 1.05–1.91). The association with BMI was somewhat stronger in women below age 50. Corresponding associations for papillary TC were similar to those for all differentiated TC. In men the only body size factors significantly associated with differentiated TC were height (non linear), and leg length (HR highest vs. lowest tertile = 3.03, 95% CI: 1.30–7.07). Our study lends further support to the presence of a moderate positive association between differentiated TC risk and overweight and obesity in women. The risk increase among taller individuals of both sexes suggests that some genetic characteristics or early environmental exposures may also be implicated in the etiology of differentiated TC.