Because of the fragmented distribution of the Karen population in northern Thailand, it is a challenge to study the shared cultural elements of the Karen's medical plant knowledge. We here document the traditional medicinal plants used by the Karen in 14 villages in Chiang Mai province, Thailand. We also attempt to determine the similarities in medicinal plant practice and the culturally important plant species between 14 Karen villages. Culturally important species are those that used by a large number of people for the same category of medicinal use (Heinrich et al., 1998).