We report the cytogenetic results obtained in 81 multiple myeloma (MM) patients with abnormal karyotypes. Most karyotypes were complex with numerical and structural abnormalities but the analysis of chromosomal abnormalities allowed identification of two cytogenetic patterns depending on the chromosome number: a first hyperdiploid pattern (54%) with recurrent trisomies 3, 5, 7, 9, 11, 15 and 19 and a second pattern (46%) showing either pseudodiploid, hypodiploid or near-tetraploid karyotypes. Structural abnormalities were present in all but five hyperdiploid karyotypes, and frequently involved lymphoid breakpoints: immunoglobulin gene regions (36 cases) or chromosome 11q13 region (21 cases). Numerous other structural aberrations were detected; the most frequent involved chromosome 1 and chromosome 13. Structural abnormalities were significantly more frequent in the second hypodiploid group. When analyzing the results obtained in the 60 patients studied at the time of diagnosis, a prognostic correlation was found between the cytogenetic pattern and overall survival: hyperdiploid patients had a longer survival than patients belonging to the pseudo/hypo/near-tetraploid group (median survival 36.8 vs 18.2 months, P < 0.04). These results suggest that MM could correspond to two closely related diseases.