Mutations in the Ganglioside-induced differentiation-associated protein-1 (GDAP1) gene cause autosomal recessive Charcot-Marie-Tooth disease type 4A. The protein encoded by GDAP1 shows clear similarity to glutathione transferases (also known as glutathione S-transferases or GSTs). The human genome contains a paralog of GDAP1 called GDAP1L1. Using comparative genomics, we show that orthologs of GDAP1 and GDAP1L1 are found in mammals, birds, amphibians, and fishes. Likely orthologs of those genes in invertebrates and a low but consistent similarity with some plant and eubacterial genes have also been found. We demonstrate that GDAP1 and GDAP1L1 do not belong to any of the known classes of GST genes. In addition to having distinctive sequences, GDAP1 and its relatives are also characterized by an extended region in GST domain II, absent in most other GSTs, and by a C-terminal end predicted to contain transmembrane domains. Mutations affecting any of those characteristic domains are known to cause Charcot-Marie-Tooth disease. These features define the GDAP1 class of GST-like proteins.