A meta-analysis was conducted to determine the effects of exercise on health-related physical fitness of individuals with an intellectual disability. The data came from 21 individual studies yielding 100 effect sizes (ESs). Large effects were demonstrated for muscular and cardiovascular endurance, moderate for muscular strength, and small for flexibility. No significant effects were found for body composition. Document source and program length influenced muscular and cardiovascular endurance outcomes, as published studies and longer programs produced larger ESs. In addition, program type influenced muscular strength (resistance programs produced larger ESs than combined programs), and program frequency influenced flexibility (higher frequency programs had larger ESs than lower frequency programs). It was concluded that additional research is needed to investigate means to improve body composition, flexibility, and muscular strength. Future studies should upgrade their standards for reporting appropriate statistical information and information related to sample and exercise prescription components.