Territorial spacing is an aspect of songbird territoriality which is easily investigated, though often ignored. Cerulean warblers (Dendroica cerulea) maintain all-purpose breeding territories in eastern North American deciduous forest. Many observers have noted that cerulean warblers may breed in clusters of territories, but this information has not been determined statistically. We investigated the spatial relationships of cerulean warblers at Big Oaks National Wildlife Refuge, Madison, Indiana, during the summers of 2002 and 2003. We used a nearest neighbor analysis for the spatial placement of the centroids of cerulean warbler territories. The analysis indicated that clustering occurred in three out of the five study plots. Territories which exhibited clustered distribution had significantly higher amounts of vegetative stratification, more trees, and trees with smaller diameter than territories which were not clustered.