We describe two patients who received haematopoietic stem cell marrow transplantation, and developed male genital lichen sclerosus (MGLSc), one of whom also had squamous carcinoma in situ (Bowen disease). MGLSc has previously been associated with graft-versus-host disease. Various aetiological factors for LSc have been proposed, including a role for chronic occluded epithelial exposure to urine. A number of factors imply that the risk of malignant transformation in this bone marrow transplant group is likely to be higher than the overall figure of 2–9% cited for MGLSc. It is vital, therefore, that clinicians involved in the care of those with haematological malignancies are adequately prepared to examine the genitals of their patients, and to recognize and refer any suspect penile lesions.