In acute aortic dissection (AAD), timely diagnosis is challenging. However, dedicated studies of the entity and determinants of delay are currently lacking. We surveyed pre-/in-hospital time to diagnosis and explored risk factors for diagnostic delay. We analyzed the dedicated database of a metropolitan AAD network (161 patients diagnosed since 1996; 115 Stanford type A) in terms of hospital arrival times (from pain to presentation at any hospital) and in-hospital diagnostic times (presentation to final diagnosis). Median (interquartile range) in-hospital diagnostic times were approximately twofold greater than hospital arrival times (177 minutes, 644, vs 75 minutes, 124, p = 0.0001, Wilcoxon test). Median annual in-hospital diagnostic times were most often approximately 3 hours (spread was wide, but decreased after 2001; rho = -0.94, p = 0.005). Risk factors (univariate analysis) for in-hospital diagnostic time >75th percentile (12 hours) included pleural effusion (odds ratio 3.96, 95% confidence interval 1.80 to 8.69), dyspneic presentation (odds ratio 3.33, 95% confidence interval 1.93 to 8.59), and age <70 years (odds ratio 2.34, 95% confidence interval 1.03 to 5.36). Systolic arterial pressure < or =105 mm Hg decreased the likelihood of lengthy diagnosis (odds ratio 0.08, 95% confidence interval 0.01 to 0.59). In patients (n = 82) with routine values (since 2000), troponin positivity (odds ratio 3.63, 95% confidence interval 1.12 to 11.84) and an acute coronary syndrome-like electrocardiogram (odds ratio 2.88, 95% confidence interval 1.01 to 8.17) were also risk factors. In conclusion, in a metropolitan setting, most of the diagnostic delay may occur in hospital. At presentation, pleural effusion, troponin positivity, acute coronary syndrome-like electrocardiogram, and dyspnea are possible "clinical confounders" associated with particularly long in-hospital diagnostic times.