Drawing upon Self-Determination Theory, the purpose of our study was to examine the motivational determinants of older women's dropout and participation in physical activity (PA). Older women who dropped out (n = 242) or remained (n = 332) in an organized PA program completed the Sport Motivation Scale as well as health and PA measures. We found that women who dropped out presented lower levels of self-determined motivations and higher levels of amotivation than persistent women. Cluster analyses revealed three motivational profiles among persistent participants: "High Combined" (high levels of self-determined motivation and introjected regulation as well as moderate levels of external regulation), "High Introjected" (moderate scores of self-determined motivation and high introjected regulation as well as low scores of external regulation), and "Moderate Introjected" (low levels of self-determined motivation, moderate levels of introjected regulation, and low levels of external regulation). Our study adds to our understanding of motivational processes and of older women's participation in and withdrawal from PA. It revealed that different motivations could drive active older women's engagement in PA, and it provided support for a person-centered approach in which distinctive combinations of motivations emerged among different groups of active older women. The messages delivered in order to promote PA may account for the multidimensionality of motivation and may be oriented toward different purposes, tapping into different forms of motivation and informing the design of interventions aimed at promoting women's health. (Contains 3 tables and 1 figure.)