The Brazilian fitness centers market serves 2.8 million people and might have generated revenues of approximately R.8 billion in 2003 (ACAD, 2003). Seven thousand stablishments, from small to large fitness centers, competed for the customer s attention, who are in search of a healthier life and a perfect body. Authors such as Oliver (1999) and Reichheld (1996) state that the adoption of a loyalty strategy offers a positive impact on profits and allow a gradual increase of the customer retention rate. This dissertation evaluate the existence of loyalty in the fitness centers market, identify the characteristics of the loyalty behavior and analyse if there are differences in loyalty behavior between the youth segment (less than 50 years old) and the elderly segment (50 years old or more). The study was conducted using the Oliver (1999) construct and it has identified that both segments are loyal, although they showed emphasis in different characteristics. The younger consumers` loyalty presents relationship with affective aspects. The elderly segment appeared to have a connection between its loyalty behavior and the conative aspects.