Mature fat tissue can be found in both benign lesions and neoplasms of the thyroid gland. The pathophysiology of adipose tissue infiltration in the thyroid gland is not clear. Three cases of diffuse lipomatosis and two cases of thyroid papillary microcarcinoma containing mature fat in their stroma were diagnosed between 2002 and 2009 years. These five cases are presented in this report with a review of lipomatous lesions in the literature.