We present an interesting image of a painless growing mass of the right arm in a 76-year-old man. A musculoskeletal MRI of the right arm showed a 7.5 × 3-cm homogeneous, well-defined mass, elongated along the course of muscle fascias and independent of the adjacent bone. A core-needle biopsy was performed, and the diagnosis of low-grade follicular lymphoma was established. Intramuscular lymphoma should be integrated into the differential diagnosis of tumors surrounding neurovascular structures, alongside peripheral nerve tumors and soft tissue sarcoma. MRI and whole-body 18F-FDG PET/CT features provided useful information to refine differential diagnosis in this case.