Focal myositis. A new cause for the pediatric neck mass. Focal myositis is an inflammatory pseudotumor of skeletal muscle that may involve the head and neck. It can closely mimic either a neoplastic or infectious process. We present the case of a 7-year-old boy with a 2-week history of a painful, unilateral neck swelling, fever, and torticollis. He failed to respond to antibiotic therapy and required an open neck exploration. An incisional biopsy of the indurated, inflammatory tissue adherent to his sternocleidomastoid muscle showed focal myositis. Focal myositis is an unusual, but important possibility in the differential diagnosis of any neck mass and especially one in a child. Although its cause is unknown, it is a self-limited disease and neither excisional biopsy nor radical resection is justified. 