The paper presents an integrated approach to least-cost generating unit maintenance scheduling for interconnected power systems. A mixed integer programming (MIP) model is developed which analyses the fuel supply decisions, generation and maintenance scheduling decisions as well as inter-utility transfer schedules in a comprehensive way. The method is applied to two interconnected Indian utilities. Firstly, the impact of fuel supply constraints and hydro energy availability on maintenance scheduling has been examined for one utility. The analysis has been extended to develop a centralized maintenance plan for both the utilities incorporating inter-utility transfer decisions. Studies reveal that the interconnected mode of operation can lead to substantial changes in fuel supply decisions and the overall system operating costs are significantly reduced.