Granulomatous slack skin is an extremely uncommon form of cutaneous T-cell lymphoma. We report a case occurring in a 29-year-old man, who had generalized, progressive skin lesions evolving to nodular swellings and folds in the flexural regions, and peripheral blood and marrow involvement. The biopsies were initially misinterpreted as xanthogranuloma or granulomatous inflammation. Histologically, the entire dermis and subcutis was infiltrated by non-necrotizing granulomas comprising mononuclear histiocytes, multinucleated giant cells and small lymphoid cells with irregularly folded nuclei, associated with loss of elastic fibres. The small lymphoid cells showed focal epidermotropism. Immunohistochemical studies showed that they were of T-lineage (CD3+, CD43+, CD45RO+). The multinucleated giant cells, which showed reactivity with the histiocytic markers CD68 and Mac387, were highlighted by intense, thick membrane staining with CD45, CD43 and CD45RO. Ultrastructurally, they exhibited features of macrophages with numerous surface villous processes and lysosomes. Greater awareness of this entity may facilitate more prompt and accurate diagnosis, obviating a futile search for a non-existent infective aetiology.