Objectives: The objective was to evaluate a new mechanism for reporting and classifying patient safety events to increase reporting and identify patient safety priorities. Methods: A voluntary patient safety event reporting system accessible by all health care workers was implemented in the Cardiothoracic Intensive Care and Post Anesthesia Care Units. Information collected included patient identifiers; date, time, and location of report and event; type and description of event; and severity score. Narrative descriptions of events were analyzed and coded to describe when in the care process the event occurred, what occurred, and a causal classification of why the event occurred. Results: A total of 163 reports describing 157 events were received. These included 121 events reported from the intensive care unit (25.3 reported events per 1000 patient-days), a 3-fold increase compared with the preexisting on-line reporting system. A total of 113 reports (69%) came from nurses, 31 from physicians (19%), and 10 from other staff (6%). A majority of events (85, 54%) reached the patient but caused no harm. Multiple causes were identified for the majority of events. The most frequent causes were related to human factors (48%) and organizational factors (34%). Conclusions: Health care workers were willing to use the patient safety event reporting system, which yielded a broad range of patient safety data. Patient safety events are multifaceted and often have multiple causal factors. Application of a causal classification model for patient safety event coding in the intensive care and preoperative and postoperative care units is feasible and facilitates local communication of important event-related information.