Abstract: Pear flower bud necrosis (PFBN) has been observed in Uruguayan orchards affecting the productivity of the trees. Severity of the problem is highly variable across years and despite the fact that it is observed in several countries, the etiology of the disease is not always clear. To elucidate the cause of PFBN, different activities were implemented over several years:surveys of pear orchards to quantify PFBN severity, morphological and histological studies of diseased buds, and isolation of potential pathogenic microorganisms from affected tissues. From the orchard surveys no clear association between climatic conditions (mean temperatures, precipitation, chilling hours) and PFBN were detected for the five years evaluated. Flower buds collected one month before flowering and fixed in formalin-ethanol-acetic acid solution showed necrosis associated with tumour development in bud primordia, and histological preparations from those tumours showed cell hypertrophy and hyperplasia. Finally, from the diseased buds we consistently isolated bacteria and no fungi. The bacteria were gram negative, oxidase positive, fluorescent on King B medium, produced indole-3-acetic acid and were positive in the tobacco hypersensitivity test. We sequenced the 16S RNA genes of the isolated bacteria to perform a taxonomic classification. We conclude that PFBN in Uruguay is caused by bacteria belonging to the Pseudomonas genus. @ International Society for Horticultural Science.