Yskert von Kodolitsch,1 Julie De Backer,2 Helke Schüler,1 Peter Bannas,3 Cyrus Behzadi,3 Alexander M Bernhardt,1 Mathias Hillebrand,1 Bettina Fuisting,4 Sara Sheikhzadeh,1 Meike Rybczynski,1 Tilo Kölbel,1 Klaus Püschel,5 Stefan Blankenberg,1 Peter N Robinson61Centre of Cardiology, University Hospital Eppendorf, Hamburg, Germany; 2Centre for Medical Genetics, University Hospital Ghent, Ghent, Belgium; 3Diagnostic and Interventional Radiology Department and Clinic, 4Department of Ophthalmology, 5Department of Legal Medicine, University Hospital Eppendorf, Hamburg, Germany; 6Institute of Medical Genetics and Human Genetics, Charité Universitätsmedizin, Berlin, Germany Abstract: Three international nosologies have been proposed for the diagnosis of Marfan syndrome (MFS): the Berlin nosology in 1988; the Ghent nosology in 1996 (Ghent-1); and the revised Ghent nosology in 2010 (Ghent-2). We reviewed the literature and discussed the challenges and concepts of diagnosing MFS in adults. Ghent-1 proposed more stringent clinical criteria, which led to the confirmation of MFS in only 32%–53% of patients formerly diagnosed with MFS according to the Berlin nosology. Conversely, both the Ghent-1 and Ghent-2 nosologies diagnosed MFS, and both yielded similar frequencies of MFS in persons with a causative FBN1 mutation (90% for Ghent-1 versus 92% for Ghent-2) and in persons not having a causative FBN1 mutation (15% versus 13%). Quality criteria for diagnostic methods include objectivity, reliability, and validity. However, the nosology-based diagnosis of MFS lacks a diagnostic reference standard and, hence, quality criteria such as sensitivity, specificity, or accuracy cannot be assessed. Medical utility of diagnosis implies congruency with the historical criteria of MFS, as well as with information about the etiology, pathogenesis, diagnostic triggers, prognostic triggers, and potential complications of MFS. In addition, social and psychological utilities of diagnostic criteria include acceptance by patients, patient organizations, clinicians and scientists, practicability, costs, and the reduction of anxiety. Since the utility of a diagnosis or exclusion of MFS is context-dependent, prioritization of utilities is a strategic decision in the process of nosology development. Screening tests for MFS should be used to identify persons with MFS. To confirm the diagnosis of MFS, Ghent-1 and Ghent-2 perform similarly, but Ghent-2 is easier to use. To maximize the utility of the diagnostic criteria of MFS, a fair and transparent process of nosology development is essential. Keywords: Marfan syndrome, Ghent nosology, diagnosis, FBN1, mutation, aorta