Most unilateral head and neck masses are benign, although malignancy is a possibility in some cases. However, there are other rare causes of unilateral neck masses, such as focal myositis, which is a rare, benign condition belonging to the family of inflammatory pseudotumors of the skeletal muscles, with rare presentations in the head and neck region. Focal myositis presents as a rapidly enlarging neck mass that can be misdiagnosed by fine-needle aspiration biopsy and/or radiologic imaging as either an infective or a neoplastic process. To date, there are only 5 reported cases of adult focal myositis of the sternocleidomastoid muscle in the medical literature. In this article, the authors present 2 cases involving patients with focal myositis of the sternocleidomastoid muscle that were successfully diagnosed with core-needle biopsy and managed conservatively. The pros and cons of fine-needle aspiration biopsy and core-needle biopsy are discussed. Based on the authors' results, fine-needle aspiration biopsy universally fails to provide the diagnosis of focal myositis. In contrast, core-needle biopsy successfully diagnosed focal myositis in both of our patients. Both of them had complete resolution with conservative management.