Crataegus (Rosaceae; hawthorn), are small trees that grow in the Northern Hemisphere. Plant materials of Crataegus show promising benefits in adjunctive treatment of cardiovascular disorders, primarily attributed to flavonoids and other phenolic derivatives. 1H NMR was used in quantification of four flavonoids (naringenin, hyperoside, rutin, and vitexin-2″-O-rhamnoside) and chlorogenic acid in leaf extracts of four Crataegus species. The data were validated by comparison to HPLC-DAD. Vitexin and its derivatives were significantly more concentrated in the European (C. monogyna and C. laevigata) leaves and rutin significantly more concentrated in the North American (C. douglasii and C. okanaganensis) leaves. The concentrations of rutin and naringenin reported in this study are the highest reported for Crataegus. This work represents the first quantitative report of flavonoids in the North American hawthorns C. douglasii and C. okanaganensis and a direct comparison with the common European species.