Primary cutaneous CD4+ small/medium-sized pleomorphic T-cell lymphoproliferative disorder (PCSM-LPD) is a rare and low-grade form of cutaneous T-cell lymphoma (CTCL), representing 2% of all primary cutaneous lymphomas. Because of its rarity, the etiology or exact clinicopathology of PCSM-LPD remains unclear. We present the first case of PCSM-LPD, to our knowledge, arising at a past melanoma excision site. A 72-year-old woman with a past medical history significant for melanoma-in-situ excised 36 years ago presented to our clinic for evaluation of a single, erythematous plaque of the posterior arm within a melanoma excision scar. A biopsy was performed, revealing PCSM-LPD. Reports of the development of other T-cell lymphoproliferative disorders after prior skin trauma such as chemical burns, thermal injury, and mechanical trauma exist in the literature. Physicians should be aware of the possibility of the appearance of T-cell lymphoproliferative disorders at the site of scars or prior trauma with a time lag of months to years.