Credit default swap (CDS) has become one of the most actively traded credit derivatives, and its importance in finance markets has increased after the subprime crisis. In this study, we analyzed the correlation structure of credit risks embedded in CDS and the influence of the subprime crisis on this topological space. We found that the correlation was stronger in the cluster constructed according to the location of the CDS reference companies than in the one constructed according to their industries. The correlation both within a given cluster and between different clusters became significantly stronger after the subprime crisis. The causality test shows that the lead lag effect between the portfolios (into which reference companies are grouped by the continent where each of them is located) is reversed in direction because the portion of non-investable and investable reference companies in each portfolio has changed since then. The effect of a single impulse has increased and the response time relaxation has become prolonged after the crisis as well. Crown Copyright (C) 2013 Published by Elsevier B.V. All rights reserved.