Delirium after cardiac surgery is a risk factor for adverse outcome and even death. Disturbance of motor activity is a core feature of delirium, but hypoactive delirium often remains unrecognized. We explored wrist-actigraphy as a tool to objectively quantify postoperative recovery of 24-h rest-activity patterns to improve the early recognition of delirium after surgery. Motor activity was recorded by wrist-actigraphy after cardiac surgery in 88 patients over 65 years of age. Patients were assessed daily by using the CAM-ICU. Our final analyses were based on 32 non-delirious patients and 38 patients who were delirious on the first day after surgery. The delirious patients showed lower mean activity levels during the first postoperative night (P<0.05), reduced restlessness during the first day (P<0.05), and a lower mean activity of the 5 h with lowest activity within the first 24 h (P=0.01), as compared to the non-delirious patients. Already at a very early stage after cardiac surgery, a difference in motor activity was observed between patients with and without a delirium. As an unobtrusive method, actigraphy has the potential to be a screening method that may lead to early diagnosis and treatment of delirium.