Pseudolymphoma is a nonspecific disease characterized by lesions with lymphomatous-appearing but benign accumulation of inflammatory cells. They generally present as small ulcero-nodular lesions confined to skin which often respond to local therapies. We describe an unusual presentation of an extensive and locally aggressive cutaneous pseudolymphoma in a 21-year-old male patient who presented with extensive cutaneous eruptions gradually progressing over 6 years to involve the entire circumference of his left arm. Magnetic resonance imaging scans of his left arm showed a lesion deeply infiltrating into the soft tissue reaching up to the humerus with intense periosteal reaction. He was successfully treated with radiotherapy after many failed attempts with surgery and chemotherapy.