Here the current studies in cell DNA content of plasma cells (PC), from multiple myeloma (MM) patients is reviewed, focusing on two complementary aspects the detection of clonal abnormalities and the identification of the proliferative rate of PC. There is accumulating evidence that the measurement of cell DNA content by flow cytometry (FCM) is a useful parameter in the clinical evaluation of MM patients. Between 50 and 70% of MM patients display DNA aneuploidy, the majority of them being hyperdiploid. Comparing hyperdiploid with diploid patients, the former seem to display a better prognosis. Fluorescence in situ hybridization studies have confirmed that there is a high incidence of numerical chromosome abnormalities in MM and that trisomies are significantly more common than monosomies (84% vs 14%). The most frequent gains can be seen in chromosome 9 and 15 while the most common monosomies are those of chromosome 13 and X in females. The possibility of analysing the cell cycle distribution by using a propidium iodide (PI)/CD38 double staining technique may be an alternative to other more laborious methods of assessing the PC labelling index. Thus, patients with > 3% S-phase PC detected by FCM have an adverse prognosis and this parameter is one of the most important independent prognostic criteria for predicting survival in MM patients. Moreover, the number of S-phase PC, together with other prognostic factors, such as beta 2microglobulin, age and performance status can be a very useful tool for stratifying patients into groups in order to establish risk-directed therapeutic protocols.