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SUMMARY (1) Ficus crassiuscula, of the subgenus Pharmacosycea, has evolved the strangling habit independently of the better-known strangling figs of the subgenus Urostigma. In the windy upper regions of the Cordillera de Tilaran, Costa Rica, F. crassiuscula is a common canopy tree restricted to tall lower-montane rain forest in sheltered ravine bottoms and lee slopes. (2) F. crassiuscula has an unusual juvenile growth form, in which seedlings develop into viny saplings, rooting freely at the nodes and lacking apical dominance. This juvenile growth form can develop into sprawling thickets up to 5 m across. (3) F. crassiuscula are not distributed randomly among potential host species. They are four times as abundant on Guarea tuisana, three times as abundant on stumps, twice as abundant on Sapium pachystachys, and one-fifth as abundant on Ocotea spp. and on a Conostegia sp. as their relative stem densities would suggest. They are three to five times as abundant on Guarea spp., and half as abundant on Persea schiedeana and Ocotea spp. as expected from the host species contribution to the total forest trunk surface area. (4) Dispersal and early establishment of F. crassiuscula are not critical determinants of host preference, as viny saplings of F. crassiuscula are distributed among host species in proportion to their contribution to the total forest trunk surface area. (5) The critical stage in determining the pattern of host preference seems to involve the morphological transition from viny sapling to juvenile with an erect stem, as juveniles are four times more abundant on Guarea spp. than their relative trunk surface area would suggest. (6) The fate of viny saplings depends not only on host species, but also on how high above the ground they are established, and the locations they occupy upon their hosts. A greater proportion of adults and juveniles with erect trunks than of viny saplings is rooted more than 4m up on their hosts. Juveniles are proportionately more abundant than viny saplings on host crotches and stump tops, whilst adults are proportionately more abundant than juveniles on crotches. (7) Host size seems unimportant; F. crassiuscula is distributed among host-tree size classes in proportion to their relative trunk surface area.