RESUMEN
BACKGROUND: Nonattendance to scheduled appointments in outpatient clinics is a frequent problem in ambulatory medicine with an impact on health systems and patients' health. The characterization of nonattendance is fundamental for the design of appropriate strategies for its management. AIMS: To identify causes of nonattendance of scheduled ambulatory medical appointments by adult patients. METHODS: Case and two controls study nested in a prospective cohort. A telephone-administered questionnaire was applied within the first 72 hours to identify the causes of attendance, nonattendance, or cancellation in patients who had a scheduled appointment to which they had been present, absent, or cancelled. RESULTS: A total of 150 absences (cases), 176 attendances, and 147 cancellations (controls) in a prospective cohort of 160 146 scheduled appointments (2012/2013) were included. According to self-reports in telephone interviews, the most frequent causes of nonattendance were forgetting 44% (66), unexpected competing events 15.3% (23), illness or unwellness 12% (18), work-related inconvenience 5.3% (8), transport-related difficulties 4.7% (4), and cause that motivated appointment scheduling already resolved 4.7% (4). DISCUSSION: The main cause of nonattendance is forgetting the scheduled appointment, but there is a proportion of different causes that do not respond to reminders but could respond to different strategies.