Considerable discussion surrounds the prognostic relevance of chromosome 1 aberrations in multiple myeloma (MM), from which most important are gains of 1q21 region and deletions of 1p32 locus. Approximately 10–40% of MM patients develop extraosseous disease (EMM), where plasma cells outside of the bone marrow form tumors called plasmacytomas. Patients with EMM found at disease onset (primary EMM) represent a challenge due to a high risk of relapse and shorter survival. Patients developing plasmacytomas during therapy (secondary EMM) often experience an aggressive disease course, characterized by treatment resistance and early mortality. The exact mechanism of EMM development is not well known, but acquiring genetic alterations is one of the important hallmarks in clonal evolution, leading to EMM spread. Thus, we conducted a detailed evaluation of the distribution and clonal heterogeneity of chromosome 1 aberrations using paired samples from bone marrow and plasmacytoma tissue plasma cells. To assess the broader applicability of our findings, we performed a population-based cytogenetic analysis encompassing both EMM patients and a control cohort of MM patients without a history of EMM.