Morphological changes of plasma cells (PC) are common in multiple myeloma (MM). Loss of round or oval nuclear shape has been related to cell malignancy in human, and we looked for the occurrence of such morphological change on PC from bone marrow (BM) smears in a retrospective series of 169 MM patients at diagnosis. Nuclear shape changes of PC differed according to the patients (notch, dumb-bell, folded or monocytoid appearance), even in the same patient; all subtypes were pooled and defined as PC with irregular nuclear shape (PCIN). A significant number of PCIN (>/=5% of all BMPC) was found at diagnosis in 20.7%. Median survival was of 22 months for patients with >/=5% PCIN, and 41 months for others (p=0.0001). Significant relationship was observed with prognostic parameters related intrinsic malignancy of the tumour process but not with beta-2-microglobulin (b2m). A clear-cut relationship was found also between PCIN and hypodiploidy (p=0.0001), but not with deletion of chromosome 13. This study emphasises the relationship between PCIN, an easy-to-ascertain marker of intrinsic malignancy of the tumour process, and adverse prognosis.