We describe a 70-year-old woman with B-cell chronic lymphocytic leukaemia without nodal involvement, who developed non-Hodgkin malignant lymphoma in the toe-nails. Clinically, the affected nails looked like a typical mycotic infection, but later small tumours developed which affected the nails, and biopsy established the diagnosis. Treatment with chlorambucil (Leukeran) and prednisolone had a striking effect. Malignant infiltration of B lymphocytes in the nails is very rare, but should be considered in patients with malignant haematologic disease.