Oilseed rape cultivars possess inadequate levels of resistance to light leaf spot disease, caused by the ascomycete Pyrenopeziza brassicae Sutton & Rawlinson. High levels of resistance to this disease were found within wild accessions of Brassica oleracea and B. rapa. This resistance was introgressed into agronomically acceptable winter oilseed rape breeding lines. Seedling resistance was determined by two genes. One of these, derived from B. rapa and positioned on linkage group N1, resulted in no apparent symptoms following infection, while the other, derived from B. oleracea and positioned on N16, resulted in black necrotic flecks and a reduced amount of sporulation compared with standard cultivars. Several agronomically acceptable double haploid lines were developed which expressed very high levels of adult plant resistance.