Between October 2000 and December 2006, we located 30 nests of 25 breeding pairs of Harpy Eagle (Harpia harpyja) in the province of Darien, Panama. Most nests were in primary tropical rain forest at a mean altitude of 132 m (range  =  50–305 m). Applying the Polygon and the Maximum Packed Nest Density (MPN) methods, we estimated nest densities of 4 and 6 nests/100 km², with each breeding pair occupying 24 and 16 km² of forest, respectively. This nesting density is the highest reported for the species throughout its breeding range. Although most nests (n  =  25) were in primary forest, the average distance from small parcels (<2 ha) of agricultural fields was 2.5 km. By extrapolating the nesting density results from the selected study area in Darien to the entire area of Panama with suitable forest cover at altitudes below 350 m, we estimated that the Harpy Eagle population size could range between 806 and 1208 pairs. Greater conservation effort should be placed on potentially suitable Harpy Eagle habitat. We also suggest that educational outreach measures should be an important part of conservation efforts throughout Panama.