Research summary: This study uses the 2008 mortgage crisis to demonstrate how the relationship between vertical integration and performance crucially depends on corporate governance. Prior research has argued that the vertical integration of mortgage origination and securitization aligned divisional incentives and improved lending quality. We show that vertical integration improved loan performance only in those firms with strong corporate governance and that this performance‐integration relationship strongly decreases and actually reverses as governance quality decreases. We interpret these findings as suggesting that the additional control afforded by vertical integration can, in the hands of poorly monitored managers, offset gains from aligned divisional incentives. These findings support the view that corporate governance influences the strategic outcomes of a firm, in our case, by influencing the effectiveness of boundary decisions. Managerial summary: One of the unanswered questions of the 2008 mortgage crisis is why some firms produced toxic mortgages and others did not. Many have argued that vertically integrated banks—banks that both originated and securitized mortgages—had incentives to monitor themselves and thereby avoid overaggressive lending and outright fraud. Yet many of the worst lenders, such as Washington Mutual and New Century Financial, were in fact integrated. This study shows that the behavior of these firms critically depended on their corporate governance. We find that poorly monitored executives used their additional control over the integrated businesses to issue low quality loans that supported short‐term growth. Our results suggest that governance is a crucial prerequisite for financial services, particularly for firms whose managers control multiple, interrelated businesses. Copyright © 2015 John Wiley & Sons, Ltd.