The flavonoids present in the wastes and residues obtained during the industrial processing of lemons were characterized and quantified. Selected products of the juice-extraction line and essential-oil-recovery line were studied. Industrial lemon juice is characterized by containing hesperidin and eriocitrin as the main flavonoid glycosides (130 μg/ml), other minor flavanones and C-glycosylflavones. After the concentration process, the concentrated juice contained a 5-fold increase in the concentration of flavonoids, but some of the hesperidin present in the initial juice was lost. The flavanone glycosides were mainly concentrated in the peel and solid residues, where hesperidin was present as the prevailing flavonoid with concentrations of up to three times higher than those of eriocitrin. In liquid residues eriocitrin was the main flavonoid. The solid residues (peel and frit precipitates) were the most interesting sources for the industrial recovery of flavonoids (13 kg/t processed lemons).