The authors submit the results of cytogenetic examination of 56 patients with multiple myeloma. Chromosome changes were found in 25, i.e. 45% patients. Structural changes were found most frequently in chromosomes no. 1, 11 and 14, numerical changes in chromosomes 3, 4, 9, 11, 14, 16, 19, 21, 22, X and Y. Marker chromosomes were present above all in hyperdiploid mitoses. The authors did not detect a relationship of chromosome changes and the type of produced monoclonal immunoglobulin, nor a statistically significant difference in the frequency of chromosomal changes in treated and untreated patients. Hyperploidy and complex rearrangements of chromosomes were observed mainly during progression of the disease. In three of four patients with developed secondary plasmocellular leukaemia the authors found a chromosomal change 14q+, in two as a result of translocation 11/14.