Abnormalities of chromosome 1 are among the most frequent chromosomal aberrations in patients with multiple myeloma (MM) and are considered a poor-risk genetic feature. To define the frequency and minimal region of 1q gain, we performed immunophenotyping and fluorescence in situ hybridization, comparative genomic hybridization (CGH), and array-CGH in 30 patients in relapse and progression of MM. Gain of 1q21 was found in 15 patients (50%), and in 14 of them whole-arm gain was found. One of these 14 patients had trisomy of chromosome 1 together with whole arm 1q gain, and two others had segmental duplication together with whole arm 1q gain. Segmental duplication of 1q21.1 approximately q23.1 alone was found in one patient. These results confirmed a high frequency of 1q aberrations and revealed that the vast majority of patients with 1q aberration in relapse and progression of MM display whole arm 1q gain. Finally, we observed that 1q gain is highly associated with number of additional changes.