Lianas (woody vines) contribute substantially to the diversity of woody plants in Yasuní National Park, Eastern Ecuador. In total 606 individuals, belonging to 138 species, were found in two 20-m × 100-m plots. The liana diversity was higher than in any comparable study, but the density was relatively low. Sapindaceae and Leguminosae were the most species-rich families, whereas Leguminosae and Celastraceae were the most abundant families. The number of liana individuals as well as the number of liana species was partially explained by forest structure, but 92% of the variation in number of liana species depended on the number of liana individuals. Areas with high density of small trees had high liana density, and areas with a high number of tree saplings had a relatively high diversity of climbing lianas. The probability of trees being colonized by lianas increased with tree diameter. The presence of one liana on a tree increased its risk of being colonized by additional lianas.