Angioimmunoblastic T-cell lymphoma (AILT) is a histopathologically well-defined entity. However, despite a number of cytogenetic studies, the genetic basis of this lymphoma entity is not clear. Moreover, there is an overlap to some cases of peripheral T-cell lymphoma unspecified (PTCL-u) in respect to morphological and genetic features. We used array-based comparative genomic hybridization (CGH) to study genetic imbalances in 39 AILT and 20 PTCL-u. Array-based CGH revealed complex genetic imbalances in both AILT and PTCL-u. Chromosomal imbalances were more frequent in PTCL-u than in AILT and gains exceeded the losses. The most recurrent changes in AILT were gains of 22q, 19, and 11p11–q14 (11q13) and losses of 13q. The most frequent changes in PTCL-u were gains of 17 (17q11–q25), 8 (involving the MYC locus at 8q24), and 22q and losses of 13q and 9 (9p21–q33). Interestingly, gains of 4q (4q28–q31 and 4q34–qtel), 8q24, and 17 were significantly more frequent in PTCL-u than in AILT. The regions 6q (6q16–q22) and 11p11 were predominantly lost in PTCL-u. Moreover, we could identify a recurrent gain of 11q13 in both AILT and PTCL-u, which has previously not been described in AILT. Trisomies 3 and 5, which have been described as typical aberrations in AILT, were identified only in a small number of cases. In conclusion, CGH revealed common genetic events in peripheral T-cell lymphomas as well as peculiar differences between AILT and PTCL-u. © 2006 Wiley-Liss, Inc.