1. Knowledge of global diversity patterns is important for research into the factors that shape them, and for systematic conservation planning. However, most species inventories are incomplete and biased towards conspicuous, charismatic, geographically widespread, and temperate species. These biases hamper attempts to gain a clear view of underlying diversity patterns, and compromise conservation plans that are based upon what is known.2. Here we investigate this problem using two methods to estimate species diversity in the parasitic wasp family Braconidae. The first quantifies the effect of taxonomic revisions on species numbers within genera to estimate the present level of underdescription. The second additionally considers the numbers of specimens referred to in descriptions and revisions.3. Modelling underdescription as a function of region and body size shows that research carried out thus far displays significant geographical and taxonomic biases.4. Correcting for these biases affects the distribution of inferred undiscovered diversity among braconid subfamilies and among regions, as well as the total diversity estimates for the family.5. The geographic distribution of levels of underdescription also has implications for latitudinal diversity gradients. Weak or non-existent gradients in some taxa may be caused simply by differences in the number of undescribed species between tropical and temperate regions.6. Such analyses can enlighten researchers as to where, taxonomically and geographically, research should be directed to economically improve species richness estimates. In the case of braconid wasps the greatest gains are to be made in Africa and southern America, and for the Braconinae and Microgastrinae.