When an expensive one unit system fails or breaks down, it is often more practical to perform ″minimal repair″ than to make a replacement or perform a complete overhaul. Instead replacements or complete overhauls are made periodically at fixed multiples of some predetermined time T. In this work the authors treat a model for this minimal repair-periodic replacement policy, and consider the problems of determining: (1) the period T which minimizes the total expected cost of repair and replacement over a fixed time horizon (0,t), and (2) the periof T which minimizes the total expected cost per unit time over an infinite time horizon.