We aimed to investigate the incidence and density of Demodex folliculorum in adults with leukaemia or lymphoma. Fifty patients with haematological malignancy and 50 healthy controls were studied. Patients had been diagnosed with acute lymphocytic leukaemia (12%), acute myelocytic leukaemia (32%), chronic lymphocytic leukaemia (4%), chronic myelocytic leukaemia (10%), Hodgkin's lymphoma (4%) or non-Hodgkin's lymphoma (38%). Standardized skin surface biopsies were taken and greater than or equal to 5 living parasites/cm(2) of skin was defined as an infestation. The difference in infestation rates between patients and controls was statistically significant. The highest incidences of D. folliculorum were found in patients with acute myelocytic leukaemia (10%), non-Hodgkin's lymphoma (6%), acute lymphocytic leukaemia (4%), chronic lymphocytic leukaemia (4%) and chronic myelocytic leukaemia (4%). Demodicidosis should be included in the differential diagnosis of facial eruptions in patients with haematological malignancies who are receiving chemotherapy, and a standardized skin surface biopsy should be performed.