Prime brokers play an important role in intermediating arbitrage capital to hedge funds. A fund’s peer-group ranking, relative to funds that share the same prime broker, significantly affects how investors respond to its past performance. I decompose the standard performance-flow relationship into two components: (1) flows that respond to overall performance rank, and (2) flows that respond to relative (within prime broker) performance rank. Strong relative rank drives fund in-flows, while poor overall rank drives out-flows. These results suggest that prime brokers intermediate about 40% of the standard performance-flow relationship.