In Italy, some of the highest incidence rates (IRs) of thyroid cancer (TC) worldwide have been reported. TC cases <85 years of age reported to Italian cancer registries during 1991–2005 were included. Age-standardized IRs were computed for all TC and age–period–cohort effects were estimated for papillary TC. IRs of TC were twofold higher in 2001–2005 than in 1991–1995 (18 and 8 per 100000 women, 6 and 3 per 100000 men, respectively). Increases were similar in the two sexes and nearly exclusively due to papillary TC. Increases of papillary TC by birth cohort were found in both sexes and among all age groups between 20 and 79 years. Age–period–cohort models showed a strong period effect in both sexes (rate ratio for 2001–2009 versus 1991–1995 = 2.5 in women and 2.3 in men), although IRs peaked at an earlier age in women (45–49 years) than men (65–69 years). The strength of the period effect in both sexes and the earlier onset in women than men strongly implicated increased medical surveillance in the upward trends of papillary TC incidence in Italy. The consequences of the current intense search for TC on morbidity and possible overtreatment, especially among young women, should be carefully evaluated.