Parthenolide, a biologically active sesquiterpene lactone found in feverfew [Tanacetum parthenium (L.) Schultz Bip., Asteraceae], has been indirectly linked to the anti-migraine action of feverfew preparations. Commercial preparations of feverfew leaves are known to vary widely in parthenolide content. Thirty-one feverfew accessions of diverse origin were examined for morphological traits and parthenolide content. Significant variation in parthenolide content was found among the populations. Mean parthenolide levels ranged from non-detectable to 1.68% +/- 0.97 (per dry weight) based upon HPLC-UV-MS. In general, feverfew plants grown from wild-collected seed from botanical gardens and the USDA accessions had higher mean parthenolide levels (0.72% +/- 0.57) than plants from commercial sources, including the generic material (0.34% +/- 0.23) and cultivars (0.35% +/- 0.40). Feverfew varieties with a light green/yellow leaf color had significantly higher mean parthenolide levels (1.61% +/- 0.61%) than darker-leafed varieties. A significant positive correlation between days to anthesis and parthenolide content was observed. Parthenolide levels did not correlate with floral morphology. This study shows that further selection for improved horticultural attributes and natural product content has potential to improve feverfew for the botanical/medicinal plant industry.