Between 2001 and 2002, plant collections from wild populations of Norwegian tansy (Tanacetum vulgare L.) were studied with a focus on essential oil (EO) yield and composition in order to characterize the chemotypical EO variability. Tansy collections of 40 different locations from North, Mid-, and South Norway were transplanted to the Apelsvoll Research Centre Div. Kise in 2000 and grown for 2 years before the aerial parts (leaves and flower buds) were harvested in June 2002. The EO from individual plants was isolated from dried plant material by hydrodistillation and analyzed by gas chromatography-mass spectrometry (GC-MS) on a DB5 column at the Plant Biocenter. The EO yield ranged between 0.35 and 1.90% (v/w) (average: 0.81%); the most abundant thujone plants were especially rich in EO volatiles (0.95%). On the basis of GC-MS data, seven chemotypes could be identified as follows: A, alpha-thujone (two individuals); B, beta-thujone (22); C, camphor (six); D, chrysanthenyl acetate/chrysanthenol (three); E, chrysanthenone (two); F, artemisia ketone/artemisia alcohol (three); and G, 1,8-cineole (two). The thujone chemotype was dominated by beta-thujone (81%) associated with alpha-thujone, but tansy plants rich in alpha-thujone were also detected (61%). The chemotypical classification of Norwegian tansy genotypes was underscored by preliminary studies from 2001, indicating the genetic uniformity and biochemical stability of the domesticated plants.