We describe four patients with erythrodermic cutaneous T-cell lymphomas (two with erythrodermic mycosis fungoides, and two with Sézary syndrome) who presented with extensive hypopigmented lesions that occurred during flares of their cutaneous disease. These cases must be distinguished from previously described hypopigmented mycosis fungoides where hypopigmented lesions were the sole manifestation of the lymphoma. In two cases a biopsy was performed on hypopigmented skin, showing an infiltrate of atypical lymphocytes with epidermotropism and absence of melanocytes, as in vitiligo. It is suggested that the hypopigmentation could be due to the cytotoxicity of tumour or reactional lymphocytes directed against melanocytes.