['To determine whether and to what extent the lower mortality rates for patients undergoing abdominal aortic aneurysm (AAA) repair in high-volume hospitals is explained by better nursing.', 'State hospital discharge data, Multi-State Nursing Care and Patient Safety Survey, and hospital characteristics from the AHA Annual Survey.', 'Cross-sectional analysis of linked patient outcomes for individuals undergoing AAA repair in four states.', 'Secondary data sources.', 'Favorable nursing practice environments and higher hospital volumes of AAA repair are associated with lower mortality and fewer failures-to-rescue in main-effects models. Furthermore, nurse staffing interacts with volume such that there is no mortality advantage observed in high-volume hospitals with poor nurse staffing. When hospitals have good nurse staffing, patients in low-volume hospitals are 3.4 times as likely to die and 2.6 times as likely to die from complications as patients in high-volume hospitals (p < .001).'] Is lower mortality for abdominal aortic aneurysm repair in high-volume hospitals contingent upon nurse staffing?