Brown rot (Monilinia laxa (Aderhold & Ruhland)) blossom blight and fruit rot incidence were evaluated on three sour cherry (Prunus cerasus L.) cultivars ('Kántorjánosi', 'Ujfehértói fürtös', 'Érdi botermo') in an organic sour cherry orchard in Hungary in 2003 and 2004. Trees were grown according to the organic fruit production guidelines and small untreated plots were set up for each cultivar in both years. Blossom blight and fruit rot were the highest on 'Érdi botermo' in both years. In 2003, both blossom blight and fruit rot incidences were low even in the untreated plots (less than 15% and 5%, respectively). In 2004, brown rot incidence reached 55% for blossom blight and 25% for fruit rot in the untreated plots. Blossom blight incidence was 1.5 to 2 times higher on 'Érdi botermo' compared to 'Kántorjánosi' or 'Üjfehértói fürtös'. During 80% of the 'Érdi botermo' bloom period, weather was rainy and cold, therefore, resulting in severe blossom and serious twig blights in the untreated plots (up to 55%). Only half as much damage was found in those organic plots that were treated with three fungicide applications during the bloom. Fruit rot incidence was highly related to rainfall during fruit maturation in 2004. Right before the harvest of'Érdi botermo', due to an intensive rainy period, about 35% of the fruit were cracked, which resulted in up to 25% infection of M. laxa on the harvested fruit. Fruit rot incidence was no more than 5% on 'Ká ntorjánosi' and 'Üjfehértói fürtös'.