AIMS: Administrative discharge codes are widely used in epidemiology, but the specificity and sensitivity of this coding is unknown and must be validated. We assessed the validity of the discharge diagnosis of syncope in administrative registers and reviewed the etiology of syncope after workup.METHODS AND RESULTS: Two samples were investigated. One sample consisted of 5262 randomly selected medical patients. The other sample consisted of 750 patients admitted or seen in the emergency department (ED) for syncope (ICD-10: R55.9) in three hospitals in Denmark. All charts were reviewed for baseline characteristics and to confirm the presence/absence of syncope and to compare with the administrative coding. In a sample of 600 admitted patients 570 (95%) and of 150 patients from ED 140 (93%) had syncope representing the positive predictive values. Median age of the population was 69 years (IQR: ±14). In the second sample of 5262 randomly selected medical patients, 75 (1.4%) had syncope, of which 47 were coded as R55.9 yielding a sensitivity of 62.7%, a negative predictive value of 99.5%, and a specificity of 99.9%.CONCLUSION: ED and hospital discharge diagnostic coding for syncope has a positive predictive value of 95% and a sensitivity of 63%.