This paper analyzes the relationship between firm efficiency and vertical integration in the Italian machine tool (MT) industry. A theoretical model of entry and competition within an industry has been set up. In this model firms can choose either to be vertically integrated or not: the most efficientfirms self-select in being vertically integrated, while less efficientfirms prefer a disintegrated structure and they both coexist in equilibrium. In the second part of the paper the relationship between efficiency and vertical integration has been tested using a stochastic frontier framework in an novel panel dataset including around 500 MT builders. The theoretical prediction is confirmed: outsourcing seems a rational choice for less efficient firms to make positive operating profits and stay in the market; on the other hand, more efficient firms exploit their efficiency advantage to control a greater part of the production chain, possibly benefiting from greater coordination among different phases and tailored intermediate inputs.