Little is known about the cytogenetic features and molecular mechanisms behind hairy cell leukaemia (HCL), despite the advances in diagnosis and treatment. Therefore, we used high-resolution genome-wide array-based comparative genomic hybridisation (array-CGH) and multiplex ligation-dependent probe amplification (MLPA) to characterise copy number alterations (CNAs) in DNA from 13 cases of HCL. We also summarise CNAs and cytogenetic features in 109 HCL cases comprising our 13 cases and 96 cases from the literature. Genomic array-CGH revealed imbalances in two out of 13 cases in addition to previously described copy number variants (CNVs) found in healthy individuals. In one case, a 700 kb deletion of 20q11.22 was detected encompassing ten characterised genes, among them the TP53INP2, DNCL2A and ITCH genes. In the second case, trisomy 5, and a deletion of 5p15.2 encompassing a non-characterised gene AY328033 was found. Altogether only 20/81 (25%) of all cases studied by CGH or gene dose array revealed CNAs. The most common recurrent deletions and breakpoints were 14q22–32 (33%), 6q25 (16%), 2p12 (10%), 22q11 (10%), 17p11–13 (10%), 7q32–36 (9%), 18q11–13 (7%), 1q32–44 (6%), 8p22–23 (6%) and 7q11 (6%). Trisomy 5 occurred in 15%. In addition, several other recurrent breakpoints were identified. Although a number of genomic imbalances were identified in the HCL samples, the genome appeared remarkably stable.