The risk of cancer was examined in a cohort of 57,326 individuals who were discharged from a Danish hospital with a diagnosis of myxedema, thyrotoxicosis, or goiter. Although the general risk of cancer was only slightly increased, the risk of several sites was significantly above expected. The risk of thyroid cancer especially, was increased with standardized incidence ratios among women of 2.1 (myxedema), 2.5 (thyrotoxicosis), and 6.6 (nontoxic goiter). The increase in risk was present even many years after discharge, indicating that surveillance was not the only explanation. Furthermore, an increased risk was noted for cancer of the kidney in women discharged with myxedema (standardized incidence ratios [SIR] = 1.8) and thyrotoxicosis (SIR = 1.3), for cancer of the bladder in women discharged with myxedema (SIR = 1.5) and nontoxic goiter (SIR = 1.3), and for cancer of the hematopoetic system in women discharged with myxedema (SIR = 1.4) and nontoxic goiter (SIR = 1.4). The findings indicate that thyroid disorders may be related to cancer risk of several specific sites other than the thyroid.