The effect of storage on the total polyphenol content and individual phenolic compounds as well as on the hydrophilic antioxidant capacity of ketchups and tomato juices was studied. The total polyphenol content was determined using the Folin-Ciocalteu assay, and the antioxidant capacity of the hydrophilic fraction was determined using DPPH and ABTS(+) assays. Individual polyphenols were identified and quantified using liquid chromatography/electrospray ionization tandem mass spectrometry on a triple quadrupole. All analyses were carried out for ketchups and tomato juices after storage for 3, 6, and 9 months. The total polyphenol content and antioxidant capacity of the hydrophilic fraction decreased during storage of ketchups and tomato juices. Ketchups, in general, showed a slightly greater stability during storage than tomato juices. The most significant decrease was observed for quercetin followed by caffeic and ferulic acids, whereas glycosilated polyphenols showed greater stability during storage.