This study examined strategic deviance by firms under uncertain environments and its implications for firm performance. During the 1980s, when deregulation of the financial industry was being implemented in earnest, this study investigated the relationship between strategic choices and firm performance among U.S. banks, formulated additional hypotheses regarding the moderating effect of firm size on this relationship, and tested them through empirical research. By estimating a fixed-effects model on eight years of panel data beginning in 1983, the results showed that in an industry context characterized by high institutional environmental uncertainty, the management performance of bank holding companies was positively correlated with strategic deviance. Additionally, the results demonstrated that the impact of strategic deviance on firm performance was moderated by firm size. Based on the empirical findings, the study discussed the implications of strategic choices by firms under uncertain environments and presented directions for future research.