The tree line ecotone in the Himalayas is shaped by diverse topographic and climatic conditions. Variation in forest structure may influence ecosystem functions but so far have remained unexplored. We assessed the forest structure and its complexity across the tree line ecotone at the wind- and at the leeward side of the Annapurna range. Plots (n = 90) were situated between 3500 m and 4100 m asl. The windward side receives more than 3000 mm yr^-1 rainfall while at the leeward side rainfall is only slightly higher than 100 mm yr^-1, with higher rainfall at lower elevation. At the windward side broad-leaved Rhododendron species dominated the forest while at the leeward side needle-leaved species including Pinus wallichiana were dominant. Forest structure as obtained by terrestrial laser scanning suggests that the windward side had a lower vertical structural complexity than the leeward side. Forest structure changed with elevation across the ecotone as indicated by general additive models. At the windward side, tree density, diameter, height as well as forest canopy cover and stand structural complexity declined continuously with elevation. At the leeward side, tree and stand structural attributes did not decrease until close to the tree line but then sharply declined within a short altitudinal range. Thus, our study highlights the differences between rainfall regimes and underscores the importance of elevation for stand structural complexity across the tree line ecotone.