Technical Abstract: Interest of the scientific community in the types and levels of flavonoids in foods continues because of consistent evidence regarding beneficial effects of dietary flavonoids. Association of reduction in the risk of cardiovascular diseases and flavonoids is more convincing than the prevention of cancer, although some evidence for the reduction of some organ-specific cancers is reported. The mechanisms of action of flavonoids are not completely elucidated yet, but their antioxidative and some enzyme induction capabilities (e.g. nitric oxide synthase) are recognized to influence the beneficial effects. The Nutrient Data Laboratory (NDL) of ARS/USDA released the first flavonoids database (USDA Database for the Flavonoid Content of Selected Foods) in March 2003. At that time limited data existed for the U.S. foods in the database. Therefore nationally representative samples of 59 fruits, vegetables and nuts were procured through the Nutrient Data Laboratory¿s (NDL) National Food and Nutrition Analysis Program (NFNAP) and were analyzed by the Food Composition Laboratory (FCL) of ARS/USDA. A large volume of analytical data on food flavonoids has also been published internationally since the first release of the USDA¿s flavonoids database. Approximately 260 articles published since 2002 were retrieved through literature searches and reviewed. One hundred and two articles containing analytical data were critically evaluated to assess data quality. Analytical data generated by the FCL and new acceptable literature data were combined with the data in the 2003 database. The database contains values for 26 monomeric compounds in five subclasses of dietary flavonoids: 1) flavonols (isorhamnetin, kaempferol, myricetin, quercetin), 2) flavones (apigenin, luteolin), 3) flavanones (eriodictyol, hesperetin, naringenin), 4) flavan-3-ols [ (+)-catechin, (-)-epicatechin, (-)-epicatechin 3-gallate, (-)-epigallocatechin, (-) epigallocatechin 3-gallate, (+)-gallocatechin, theaflavin, theaflavin 3-gallate, theaflavin 3¿-gallate, theaflavin 3,3¿-digallate, thearubigins], and 5) anthocyanidins (cyanidin, delphinidin, malvidin, pelargonidin, peonidin, petunidin). All the values are reported as aglycones of compounds except for catechins and theaflavins which exist as gallate esters, predominantly in tea. The mean, standard error, minimum, and maximum values per 100g edible portion (mg/100g), number of samples, confidence codes for data quality and references from where the values were taken are reported for each compound for each food. The database is available on NDL¿s website: http://www.ars.usda.gov/nutrientdata. The updated database contains data for 394 foods, about 169 more foods than the first release. Also, values for additional flavonoids compounds for some foods that were unavailable earlier were added. Scientific names were also added for all the foods. In the first version of the database approximately 70 foods had values from U.S., while the second version now contains values for approximately 190 U.S. foods. In general, values for U.S. foods agree well with the international data. Other flavonoids such as isoflavones (daidzein, genistein and glycitein) and proanthocyanidins (dimmers, trimers, 4-6mers, 7-10mers and >10 polymers) are not included in this database as separate databases for those compounds were released earlier and are available on the NDL web site. These 3 databases will provide reliable values for epidemiological studies to assess the relationship between flavonoid intakes and health benefits. Selecting the food items normally consumed in the United States, the data can now be used for studies of U.S. population.