Whereas a majority of previous research in the diversification literature has focused on the performance consequences of diversification strategy, this paper examines the reverse relationship, that is, the effects of a firm’s prior performance on the choice between related and unrelated diversification. This paper empirically tests and confirms the view that there are systematic ex ante performance differences between firms diversifying into related businesses and firms diversifying into unrelated businesses. These findings imply that ex post performance differences between related and unrelated diversifiers, often reported in previous research, are largely attributable to these ex ante performance differences, not to diversification strategy per se.