ABSTRACT. High rates of honey bee colony losses have been reported worldwide; however, data about colony loss rates in South America is scarce. This study quantified colony losses experienced in Uruguay during the 2013?2014 season and identifies the self-diagnosed causes for these losses. An estimated 2.6% of all Uruguayan beekeepers, who collectively managed 5% of the estimated 550,000 colonies in the country, responded to this survey.We found that total summer and winter losses were similar (summer 19.0% (95% CI 13.26?24.77%), winter 20.2% (95% CI 14.98?25.39)), as were the average operational losses (summer 19.8% (95% CI 14.01?25.52), winter 18.3% (95% CI 13.15?23.56%)). The total annual loss was 28.5% (95% CI 22.42?34.51%), with each beekeeper losing, on average, 28.6%(95% CI 22.52?34.61%) of the colonies in their operation. Loss rates were similar across operations of different sizes. Queen failure, diseases and parasites, and pesticides were the leading self-reported and selfdiagnosed causes of colony losses. This study is the first to document honey bee colony losses in Uruguay, establishing a baseline for future long-term monitoring. @ INRA, DIB and Springer-Verlag France, 2016