In the present study, which is a part of a clinical-epidemiological study of complications, (the Project Peri-Operative Risk, PROPER), 510 patients, admitted for elective surgery, participated. During their time in hospital, the incidence of complications was registered by nurses. Three months after surgery, the patients were asked in a questionnaire if they had, during their time in hospital or during their convalescence at home, suffered from postoperative complications. Statements by patients and health care professionals regarding the nature and frequency of complications have been compared. Our results confirm the findings that a prospective method in registering complications results in the detection of a higher incidence than if a retrospective method is used. The analysis also reveals that patients and professionals report different types of complications. They also describe complications from different perspectives and present identical complications in different terms.