Specifications in the US Code of Federal Regulations for the colour additive D&C Orange No. 5 (Colour Index No. 45370:1) limit the levels of the synthetic by-products 2-(3,5-dibromo-2,4-dihydroxybenzoyl)benzoic acid (Br2BBA) and brominated resorcinol (Br3R) as well as the level of the intermediate phthalic acid (PhthAc). The present work reports the development and application of a high-performance liquid chromatography (HPLC) method for the quantitative determination of these impurities in D&C Orange No. 5 and its lakes. Br2BBA, Br3R and PhthAc were quantified by using five-point calibration curves with data points that ranged from 0.010% to 0.700%, from 0.012% to 0.706% and from 0.006% to 1.383% by weight, respectively. The HPLC method was applied to the analysis of test portions from 11 lots of D&C Orange No. 5 and one lot of D&C Orange No. 5 lake submitted to the US Food and Drug Administration (USFDA) for certification.