Chronic neutrophil leukaemia (CNL) is a rare myeloproliferative disorder predominantly reported in elderly patients. We present a 15-year-old girl and a 25-year-old male with CNL. Clonal cytogenetic abnormalities were detected in both patients. One showed trisomy 21 evolving into tetrasomy 21. The second patient showed a unique chromosome aberration during blast crisis: t(2;2)(q32;p24). Both patients were successfully treated with allogeneic bone marrow transplantation (BMT). CNL should also be considered as a differential diagnosis in adolescence and young adulthood. BMT represents a potentially curative treatment option in such patients.