Purpose: This is the first presented case of relapsed PCNSL or tumour metastasis in a reconstructive flap. Methodology: A 60-year-old man was admitted to with a pre-tibial wound infection two years following Grade-IIIb open right tibial fracture. Previous management involved intra-medullary nail fixation, 2nd stage Masquelet procedure and local transposition flap for soft-tissue coverage. His history was significant for primary CNS lymphoma (PCNSL), managed with induction chemotherapy and consolidation whole brain radiotherapy. He was cleared of his PCNSL one year prior to this presentation. Results: The patient described ulceration and cellulitis of the flap that failed to respond to oral antibiotics. He underwent surgical debridement and tissue biopsy, demonstrating fibrinous material deep to the flap, no infected collection. Staphylococcus lugdunensis was cultured and histological examination demonstrated sheets of large atypical lymphocytes infiltrating necrotic connective tissue. Tumour cells showed strong immunoreactivity for B cell markers CD20 and CD79a, consistent with diffuse large B cell lymphoma. Staging FDG-PET demonstrated multiple foci of uptake in the right lower limb consistent with lymphoma, largest within the transposition flap and no further sites of distant metastasis. Limb salvage was attempted with debridement, exchange of metalware, and split thickness skin graft reconstruction once granulating. The patient underwent salvage chemotherapy with and autologous stem cell transplantation. Conclusion: Consideration of malignancy as a differential diagnosis in chronic non-healing leg wounds is essential and underlies the need for routine, histological examination of chronic wounds.