An analytical method was developed for the simultaneous quantitative analysis of 6 amines and 20 flavonoids in fruits and extracts of 30 Citrus species, including C. aurantium, near-Citrus relatives, and dietary supplements by liquid chromatography with photodiode array detection. The separation was achieved with a Phenomenex Synergi Hydro reversed-phase column using gradient mobile phase of sodium acetate buffer (pH 5.5) and acetonitrile. Elution was run at a flow rate of 1.0 mL/min and UV at 254, 280, and 330 nm. Among the amines analyzed, synephrine, the main component, was present in the levels from 0.11 to 2.0 mg/g dry weight in 21 Citrus species and 0.07 to 18.62% in dietary supplements claiming to contain C. aurantium. The flavanones and flavones were analyzed in the same Citrus samples and were species-specific. The levels of flavones were very low compared with those of flavanones. The method facilitated the simultaneous quantification of 6 amines and 20 flavonoids in various Citrus species, the distinction between the different Citrus species, and the analysis of dietary supplements containing C. aurantium.