Despite the fact that multiple myeloma is a unique entity, defined by the accumulation of malignant plasma cells, a marked heterogeneity is observed among patients (regarding biological and clinical presentation, response to treatment, or survival). Current prognostic parameters are poor predictors of response to therapy and of survival in individual patients. The application and analysis of DNA microarrays to plasma cells provide an overview of gene expression programs generated by these cells in normal and pathological conditions. Genes potentially involved in transformation process have been identified by gene profiles comparison between myeloma samples, normal plasma cells from various tissues, pretumoral plasma cells and immortalized plasma cells. We can speculate that in a near future gene expression-based classification will be used as a molecular prognostic indicator.