OBJECTIVES To evaluate the incidence of subsyndromal delirium (SSD) after cardiac surgery and its impact on clinical outcome. DESIGN In this prospective study, 506 patients were screened for SSD and clinical delirium (CD) using the Intensive Care Delirium Screening Checklist. RESULTS 150 (34%) patients were classified as having SSD and 54 (12%) patients as having CD. 2% of SSD patients developed CD. Patients' age, EuroSCORE, postoperative the Acute Physiology and Chronic Health Evaluation II, the incidences of emergency operations, and the number of aortic surgery increased from non-delirious (ND) to SSD. Intensive care unit (ICU) and hospital stays were longer in CD compared with SSD patients. ND patients did not differ from SSD patients regarding duration of ventilation, ICU stay, or hospital stay. The rate of home discharge decreased from ND over SSD to CD patients. Mortality in SSD patients did not differ from ND or CD patients. CONCLUSION SSD showed a prevalence of 34% in patients after cardiac surgery. SSD occurred independent of CD for the majority of patients. Except for a lower rate of home discharge, the clinical outcome did not differ from that of ND patients. According to our data, SSD does not represent a preliminary or resolving stage of delirium.