A 50-year-old man presented with a 5-month history of swelling over the right side of neck. The swelling was associated with dull aching pain radiating to the forearm without associated weakness of upper extremity or sensory loss. There was no history of trauma. On examination a fixed mass approximately 8×6 cm in size, smooth, firm in consistency, with ill-defined margins was present in the right posterior triangle. MRI scan of the neck revealed well-defined, lobulated, heterogeneously enhancing altered signal intensity mass at the root of neck. Debulking of the tumour was performed in view of its close proximity to the brachial plexus. Histopathology revealed aggressive fibromatosis (AF). AF is a benign fibrous neoplasm arising from fascia, periosteum and musculoaponeurotic structures of the body. AF in the head and neck region tends to be locally aggressive with a nature to invade bone and soft tissue structures.