A purified mitochondrial DNA (mtDNA) probe was used to examine restriction fragment length polymorphisms produced by six restriction enzymes (XbaI,EcoRV,AvaII,HinfI, HaeIII,MboI) in 915 brown trout from western Europe. A total of 20 composite haplotypes were found with one to seven haplotypes in individual populations. Icelandic trout samples from north, south, east, and west coast drainages showed only a single common haplotype in contrast to the high level of polymorphism found in Irish and Scottish populations. The phylogeny of mtDNA haplotypes and the pattern of haplotype distribution suggests that post‐glacial colonization of brown trout in NW Europe was more complex than the dual colonization model which has been proposed on the basis of differentialLDH‐5*allele distribution. For example, Lough Melvin (Ireland) appears to have been independe