['To determine if coronary artery bypass graft (CABG) surgery without cardiopulmonary bypass (CPB) avoids the brain swelling known to occur after CPB, to quantify these brain water compartment changes, and to identify the water shifts as due to intracellular or extracellular water.', 'Prospective, controlled, and blinded.', 'Cardiac surgical unit in a university teaching hospital.', 'Patients scheduled for CABG who were assigned to conventional (n = 10) or off-pump (n = 7) surgery according to their coronary anatomy.', 'Magnetic resonance imaging (MRI) examinations were performed 1 day before surgery and 1 hour and 1 week after CABG surgery.', 'Extracellular and intracellular water homeostasis was described quantitatively by calculating the averaged apparent diffusion coefficient of brain water using diffusion-weighted MRI. Blinded visual ordering of the images from the three examinations was performed according to brain size using conventional MRI.', 'The average diffusion coefficient of brain water increased 4.7%+/-1.5% immediately after CABG with CPB and normalized after 1 week but did not change after CABG without CPB. No focal ischemic changes were seen in either group, and no gross neurologic deficits were observed. Visual analysis showed consistent brain swelling after CPB and variable changes in those operated without CPB.'] Is increased extracellular brain water after coronary artery bypass grafting avoided by off-pump surgery?