Genetic similarities were calculated among 89 Brassica oleracea L. genotypes, which included 62 broccolis (var. italica), 16 cauliflowers (var. botrytis), and 11 cabbages (var. capitata). These entries represented a wide range of commercially available germplasm, including open-pollinated cultivars, commercial hybrids, the inbred parents of several hybrid cultivars, and 27 entries that were provided as unknowns. Sixteen random genomic clones were used as probes in Southern hybridizations to detect restriction fragment length polymorphism (RFLP). From each of the random probes, an average of four polymorphic bands were classified as to their presence or absence for each genotype. The genetic similarity between ail pairs of genotypes was calculated. A multidimensional scaling (MDS) plot indicated that the broccoli, cauliflower, and cabbage groups were clustered with very little overlap. Within groups, genetic similarity corresponded to relationships based on available pedigree information. Comparison of banding patterns between hypothetical and actual hybrids was used to correctly identify the parents of several parent-hybrid combinations. The RFLP pattern of a hybrid and one of the parents (female) were used to predict the genotype and identity of the other parent (male).