The nesting ecology of the Greater Adjutant Stork (Leptoptilos dubius), the rarest stork in the world, was studied in the Brahmaputra Valley, Assam, India during 1994-97. We made a study of nine colonies in the valley during the 1994-95 nesting season, followed by a more intensive study in two subsequent nesting seasons (1995-96 and 1996-97) of two colonies at Nagaon, in central Assam. We measured the dimensions of both nest and non-nest trees, nearest distance between nest trees, and nearest house, nearest forest, nearest road, nearest water source and nearest foraging ground from each colony. All of the colonies were near human settlements. The structure of nest trees differed significantly from non-nest trees in both the overall and the intensive studies. Number of nests was highly correlated with tree height, diameter at breast height (DBH) and canopy area. About 90% of nests were built on the top of the canopy. Storks preferred to nest in compact colonies on large, widely branched trees with thin foliage cover and nearby food sources.