We study an instance-based approach for matching hierarchical ontologies such as product catalogs. The motivation for utilizing instances is that metadata-based match approaches often suffer from semantic heterogeneity, e.g. ambiguous concept names, different concept granularities or incomparable categorizations. Our instance-based match approach matches categories based on the instances (e.g. products) assigned to them. This way we partly translate the ontology match problem into an instance (object) match problem which is often easier to solve, especially when instances carry globally unique object ids. Since concepts of different ontologies rarely match 1:1 we propose to determine correspondences between sets of concepts. We experimentally demonstrate the usefulness of such correspondences for real product catalogs.