The interdisciplinary nature of optical microelectromechanical systems (MEMS) makes its design a highly involved process. To design a device that will meet the required specifications over its entire lifetime, reliability issues must be included in the design process. This work develops a method that can be used to create a step-by-step design process involving reliability issues at every stage. The process begins by listing out the constants and constraints of the design. Taking all such constraints into account, an optical design process is outlined. The effect of individual errors is studied on a key parameter like insertion loss. This gives the designer information about which parameters the design is more sensitive to, and will help in deciding the manufacturing tolerances required in the different stages. Using all of these data, an "ideal design" is developed. A Monte Carlo analysis is carried out on that design to show the effect of errors occurring simultaneously. The work concludes with a flow chart of a suggested design process to be used when designing optical MEMS devices.