Despite the growing importance of wind energy developments in Ireland, and concerns about its potential ecological impact on birds, there is a notable lack of published scientific information in this area. As a bird of conservation concern, the Hen Harrier Circus cyaneus inhabits upland areas with potential for wind energy resources. This study assessed the breeding performance of Hen Harriers across Ireland in relation to wind farm development by analysing the breeding output from 84 nests located at varying distances from wind farms. Three measures of breeding performance were investigated: (a) nest success (the proportion of nests that fledged one or more young), (b) fledged brood size (the average number of fledged chicks per successful nest), and (c) overall productivity of breeding pairs (the average number of fledged chicks across all nesting attempts). No statistically significant relationships were found between these breeding parameters and distance of the nest from the nearest wind turbine. However, lower nest success within 1 km of wind turbines than at greater distances were sufficiently close to statistical significance, and with a sufficiently small sample size, that this difference may be of biological relevance. Nests within 1 km of wind turbines which were successful had similar fledged brood sizes to those of nests at greater distances from turbines. These findings support previous research which highlighted the importance of areas within a 1 km radius of raptor nests. Our results provide the first insight into the potential effects of wind turbines for breeding success of Hen Harriers, which should be taken into consideration in assessments of wind farm impacts on this vulnerable species. Further work is required to quantify (a) direct Hen Harrier mortality through collisions, (b) habitat loss and displacement caused by wind turbines and (c) to continue ongoing monitoring of breeding success in order to confirm whether the effect of wind farm proximity suggested here is consistent. This work will support the development of an integrated management strategy for Hen Harriers in Ireland.