OBJECTIVES: A prospective design was used to examine predictors of adherence to a physical activity intervention in older adults with compromised function. METHODS: The sample included 213 men (31.1%) and women (68.9%) with an average age of 76.53 years. RESULTS: The predictor variables accounted for 10% of the variance in percent attendance during adoption and transition, respectively. Adding percent attendance during adoption to the prediction of percent attendance during transition increased the explained variance in this phase to 21%. During maintenance, the predictors accounted for 13% of the variance in frequency of physical activity; this estimate increased to 46% when adding in percent attendance from the transition phase. DISCUSSION: These results are encouraging in that the physical activity intervention appears to have been well tolerated by diverse subgroups of older adults. The role of prior behavior in predicting downstream adherence underscores the importance of developing proactive interventions for treating nonadherence in older adult populations.