This article examines resource-partitioning theory in organizational ecology in the context of the Dutch auditing industry. The theory predicts that under certain conditions, specialist organizations will proliferate as the overall industry concentrates and becomes dominated by large generalist firms. Although Dutch auditing shows long-term trends towards market concentration and a burgeoning specialist sector, the professional service orientation of the industry presents some challenges for applying the theory. Accordingly, we first reconsider the theory in this new context. Using data on the life histories of (almost) all auditing firms ever to operate in the Netherlands, we also test the implications of the theory for exit rates of auditor organizations. Although we find substantial support for the basic theory, it is also apparent that resource-partitioning processes interact with regulatory changes in the institutional environment in interesting ways.