The maintainability aspect of some complex products has a significant role during the life cycle; it is the design attribute determining the performance of various maintenance activities such as: inspection, diagnosis, repair, and replacement. If a product has poor maintainability, the maintenance activities which have to be performed on it during its life cycle are difficult, increasing the costs, and also the time required to accomplish the maintenance tasks. An early evaluation of maintainability during the design process may help the designers to make educated design choices, also from the maintenance point of view. In this article, we present a maintainability evaluation approach based on fuzzy logic; fuzzy linguistic variables are employed in order to represent and handle the design data available early in the design process. The main reason for employing fuzzy logic principles for maintainability evaluation is the imprecision and uncertainty generally characterizing the design data available at the beginning of the design process, when design specifications and requirements are subject to change and the description of the design is incomplete. The measure of the product maintainability or maintainability index might be expressed by a fuzzy numerical value computed as the weighted mean of the criteria values used for the evaluation.