Using popular/common measures of diversification employed by industrial organization scholars (Jacquemin-Berry entropy measure) and strategy scholars (size of the primary business segment), this study examines the corporate diversification and restructuring activities of American firms (sample from the Fortune 250 list) in the 1980s and 1990s. There is empirical support for the widespread notion that in the 1980s and 1990s, firms underwent major restructuring efforts by divesting unrelated (unprofitable) businesses and strengthening their core business units and related segments. Additionally, the results illustrate the consistencies and discrepancies between the above measures.