The Adams desaturated D‐15 was designed to be administered to patients with acquired colour vision defects by simply reducing the chroma of the Munseli colours by 2 for each cap in the test. In this study, the performance of the Adams desat D‐15 in the assessment of congenital colour vision deficiencies is evaluated. The standard D‐15 and Adams desat D‐15 tests were administered to 75 congenital red‐green colour deficient subjects who had been diagnosed on the basis of their performance on the Nagel anomaloscope Mark 1. The results were analysed in terms of the direction, extent and specificity of errors and compared with the diagnosis on the Nagel anomaloscope. Of the 13 colour‐deficient subjects who made no errors on the standard D‐15, 1 failed the Adams desat D‐15 and 2 made single crossings. No colour‐deficient subject who failed the standard D‐15 made anything less than a simple inversion of adjacent caps on the Adams desat D‐15. The Adams desat D‐15 did not perform as well as the standard D‐15 in identification of the type of defect in dichromats. On the basis of these data, it is predicted that about 5% of dichromats will be mis‐classified by the Adams desat D‐15 whilst under 0.1% will be mis‐classified by the standard D‐15. However, with the anomalous trichomats, more crossings were made on the Adams desat D‐15, particularly by the milder anomals, and a diagnosis was possible in more cases. Where a diagnosis was possible, it was also correct more often with the Adams desat D‐15. The Adams desat D‐15 provides a useful sub‐classification of those who pass the standard D‐15. A choice of Munseli colours lying on confusion lines rather than by a simple universal reduction of chroma by two steps should provide a more reliable diagnosis of typ