Several studies have been conducted to identify the factors that most influence on service quality and customer satisfaction in the fitness industry. However, little attention has been dedicated to the identification of the most relevant attributes. This study aims to fulfill this gap and suggests that it is also necessary to identify the factors and the attributes which are most important concerning the perceptions of customers of fitness centers. Based on the scientific literature, a 23-item questionnaire was designed and a sample of 368 customers of four Brazilian fitness centers was considered. Factorial analysis and Quartile analysis revealed that the most important factors are related to Workout facilities & Price and Staff. The fitness equipment must be varied and in sufficient quantity, besides being in perfect working order. Special attention should be dedicated to the instructors' politeness and competence, and the accuracy of information they provide. The overall cleanliness of the fitness center and the value of service are also important.