The immigration of diverse ethnic groups over the past centuries from surrounding countries into Thailand left footprints in the genetic composition of Thai mitochondrial DNA (mtDNA) lineages. The entire mtDNA control region (1,122 bp) was typed in 190 unrelated male volunteers from the northern Thailand province of Chiang Mai following highest quality standards. For a more precise haplogroup classification, selected single nucleotide polymorphisms from the mtDNA coding region were genotyped. We found several new, so far undescribed mtDNA lineages. Quasi-median networks were constructed for visualisation of character conflicts. The data were put into population-genetic relationships with other Southeast Asian populations. Although the frequencies of the Thai haplogroups were characteristic for Southeast Asia in terms of haplotype composition and genetic structure, the Thai population was significantly different from other Southeast Asian populations. This necessitates establishing regional databases, especially for forensic applications. The population data have been submitted to the EMPOP database (www.empop.org) and will be available on publication. © 2008 Springer-Verlag.