Sequencing of a 360-nucleotide segment of the mitochondrial control region for 63 individuals from an Amerindian tribe, the Nuu-Chah-Nulth of the Pacific Northwest, revealed the existence of 28 lineages defined by 26 variable positions. This represents a substantial level of mitochondrial diversity for a small local population. Furthermore, the sequence diversity among these Nuu-Chah-Nulth lineages is greater than 60% of the mitochondrial sequence diversity observed in major ethnic groups such as Japanese or sub-Saharan Africans. It was also observed that the majority of the mitochondrial lineages of the Nuu-Chah-Nulth fell into phylogenetic clusters. The magnitude of the sequence difference between the lineage clusters suggests that their origin predates the entry of humans into the Americas. Since a single Amerindian tribe can contain such extensive molecular diversity, it is unnecessary to presume that substantial genetic bottlenecks occurred during the formation of contemporary ethnic groups. In particular, these data do not support the concept of a dramatic founder effect during the peopling of the Americas.