Hashimoto's thyroiditis has been reported to be associated with many neoplastic and nonneoplastic thyroid pathologies. This retrospective study aims to determine the demographic profile of Hashimoto's thyroiditis in Sri Lankans, document ancillary pathologies in Hashimoto's thyroiditis, and determine whether there is an increased risk of occurrence of malignancies, benign neoplasms, and nonneoplastic benign lesions in Hashimoto's thyroiditis by comparing with thyroids showing multinodular goiters, follicular adenomas, and colloid nodules. The mean age of Hashimoto's thyroiditis is 43.3 years with the majority in the 41 to 60 year age group and a female to male ratio of 10.3 : 1. This study revealed a statistically significant increase of thyroid malignancies in association with Hashimoto's thyroiditis. The association of Papillary carcinoma, Non-Hodgkin's lymphoma, and Hurthle cell adenoma with Hashimoto's thyroiditis was statistically significant.