The relationship between corporate strategies and firm performance has been one of the key debates in the discipline of Strategic Management. There are studies that analyse the moderating role that certain variables may play in that relationship. These variables tend to refer to aspects within the firm or, at the very least, within the competitive environment in which a firm operates. Nevertheless, the empirical evidence on the part the general environment plays from an economic perspective is much less common, and focuses on large corporations and on periods of economic growth. Accordingly, using a panel of 1,828 Spanish manufacturing firms of different sizes, an analysis is conducted of the differences in Return On Assets (ROA), Growth in Sales (GS) and Labor Productivity (LP) between specialised firms, those with related diversification, and those with unrelated diversification, between 2002 and 2011, in which there was a period of growth alternated with another one of economic recession. Although some superiority is noted of related diversification and specialisation over unrelated diversification, the differences between strategies are less significant in periods of economic recession, and vary according to the dimension of performance considered. These results reveal the need to consider the economic cycle as a contingent factor that affects the impact corporate strategies have on firm performance.