The authors report the clinical and biological findings of a case of a rare haematological malignant entity, morphologically characterised by a bizarre nuclear abnormality in granulocytes, consisting of exaggerated chromatin clumping and apparent fragmentation of the nucleus, with a loss of segmentation. They emphasize the coexistence of proliferative and dysplastic characteristics as a distinctive marker of this disorder and suggest it may represent a distinct rare morphological entity among the atypical chronic myeloid leukaemias, Ph1 and ber negative.