The U.S. Fish and Wildlife Service (USFWS) is relying increasingly on a multi-species, rather than the more traditional single-species, approach to recovery planning under the U.S. Endangered Species Act (ESA). Supporters of the multi-species approach note potential efficiency gains in terms of biodiversity protection and agency resources. By the end of 1998, Ͼ55% of all ESA-listed species with recovery plans were covered within multi-species plans. A recent analysis found that species within multi-species plans are significantly more likely to exhibit a declining status trend. Given this finding, we compared single-to multi-species plans and found that multi-species plans reflect a poorer understanding of species-specific biology, are less likely to include adaptive management provisions, and are revised less frequently. USFWS guidelines recommend that species be combined into multi-species plans primarily on the basis of threat similarity. We developed a threat similarity index to evaluate the USFWS's conformance with these guidelines. Nearly half of the multi-species plans failed to display threat similarity greater than that for randomly selected groups of species. We advocate the explicit use of threat similarity analyses to identify appropriate groups of species for concurrent management, thereby maximizing benefits and minimizing potential drawbacks of a multi-species approach. We conclude that, as currently employed by the USFWS, multi-species recovery plans are less effective management tools than single-species plans. Given the increasing number of species covered by multi-species plans and the problems identified with these plans, we recommend that the USFWS reevaluate its use of the multi-species approach to recovery planning.