AbstractAimThe processes leading to the assembly of ecological communities can determine their functional structure. We assess the influence of biogeographical correlates associated with species diversity gradients on the global patterns of functional diversity of island parasitoid assemblages (Hymenoptera,Braconidae). We also evaluate whether island assemblages present a non‐random functional structure.LocationFifty‐three archipelagos distributed world‐wide.MethodsSix traits related to morphology, attack strategy and development were used to measure functional diversity and determine the level of departure from randomness on trait diversity between islands and their corresponding species pool, through null models. We used generalized and partial regressions to determine the influence of different predictors (climate, regional and local island characteristics) on the functional diversity of island assemblages, comparing results with those obtained for species richness. We also evaluated whether any of the predictors or particular species traits were related to the patterns obtained when comparing island assemblages with null models.ResultsMost of the geographical variation in functional diversity was not explained by the predictors evaluated, while for species richness these explained over 70% of spatial variation. The abiotic characteristics of islands with functionally clustered parasitoid biotas (c. 40% of all islands) did not differ from those of other islands. Comparisons between functionally clustered assemblages and those expected randomly from the species pool indicated a higher percentage of that the former included proportionally fewer ectoparasitoid and idiobiont species, which attack fewer host orders and prefer the egg and larval stages of their hosts.Main conclusionsThe predictors correlated with functional diversity differ from those driving species richness patterns. We argue that biotic filters associated with the structure of the host communities may be important determinants of the assembly of many island parasitoid faunas, leading to assemblages dominated by species presenting particular ranges of trait values that differ from those in their pool of potential colonists.