Objective To investigate the feasibility of endurance exercise training in patients with small abdominal aortic aneurysm (AAA), and to obtain preliminary data of its impact on important health outcomes. Design Randomized controlled pilot study. Setting University rehabilitation facility. Participants Patients with small AAA (N=28; mean age ± SD, 72±7y). Intervention Participants were randomized to a 12-week program of moderate-intensity endurance exercise or standard care control (encouragement to exercise only). Main Outcome Measures Safety was assessed in terms of the frequency of adverse events and changes in maximum AAA diameter. Outcomes were assessed at baseline and 12 weeks including cardiopulmonary fitness (ventilatory threshold), health-related quality of life (Medical Outcomes Study 36-Item Short-Form Health Survey [version 2]), and markers of vascular risk (eg, blood pressure and high-sensitivity C-reactive protein). Results Of 545 patients contacted, 28 (5%) entered the trial. There were 3 (11%) dropouts. Adherence to the exercise program was 94%. There were no paradoxical increases in AAA size or adverse clinical events. Ventilatory threshold increased in the exercise group, but not the control group (adjusted mean difference, 2.5mL·kg−1·min−1; 95% confidence interval, 0.5–4.5; d=.82). Systolic blood pressure and high-sensitivity C-reactive protein decreased in the exercise group compared with the control group (d=.34 and d=.58, respectively). There were no substantial changes in anthropometric variables or quality of life. Conclusions Despite a low recruitment rate, the findings suggest that moderate-intensity endurance exercise training is feasible in patients with small AAA, and can evoke improvements in important health outcomes.