Sacroiliac joint involvement is not specific to seronegative spondyloarthropathies (SpA). There are some rare reports of conditions which mimic sacroiliitis. This paper reports a case of follicular thyroid carcinoma in a patient who had been referred to a rheumatology clinic with hip pain. Sacroiliac joint involvement was her presenting feature before she was correctly diagnosed. The patient was a female, 63 years of age, who referred to a rheumatologist because of unilateral hip pain. Patrick's test on her right side was positive, and the range of motion of her right hip was restricted. Imaging studies included conventional hip radiography and magnetic resonance imaging (MRI) revealed sacroiliitis with surrounding destructive lesion. In review of systems and physical examination, a thyroid nodule was found. Computed tomography (CT)-guided needle biopsy of her hip and fine needle aspiration (FNA) of the thyroid nodule established follicular thyroid carcinoma. In approach to sacroiliitis, rare differential diagnoses (besides SpA) and mimickers of sacroiliitis such as neoplastic lesions should also be considered to avoid misdiagnosis.