In this paper we present a technique for automatically generating hierarchical clusters of documents. Our technique exploits document keyphrases as features of the document space to support clustering. In fact, we cluster keyphrases rather than documents themselves and then associate documents with keyphrase clusters. We discuss alternative measures of similarity between ‘soft-clusters’ which seed Ward’s hierarchical clustering algorithm, and present the resulting cluster hierarchies that we have produced for a large collection of scientific technical reports. We analyse the effect of the alternative similarity measures and suggest improvement to our technique.