The concept of genetic conformity lies at the basis of the definition of essential derivation, or the process of using a protected variety (or `initial variety', IV) as the base to develop another similar variety (the essentially derived variety, EDV). Methods based on morphology, biochemistry or on molecular markers can be used to estimate genetic conformity. In this study, the capability of AFLP(R)(1) markers to provide a reliable and meaningful estimate of genetic conformity of different varieties was investigated in diploid perennial ryegrass (Lolium perenne spp.), an allogamous species whose varieties are genetically heterogeneous. Twelve accessions with known breeding lineage, comprising five closely related groups, were included in the study. For the set of test accessions analysed, the AFLP protocol accurately reproduced the same relationships as were evident from examining their morphology and both these results were consistent with the relationships known to exist within the different test groups. Principal components analysis as well as cluster analysis associated unambiguously the IV and the EDV accessions. It was concluded that the methodology developed in this study could be used as a model from which to create a protocol for evaluating putative cases of essential derivation.