The Marfan syndrome (MFS) is strongly associated with aortic disease causing a high prevalence of prophylactic aortic surgery, aortic dissection, and sudden death. The aim of the present study was to evaluate mortality in a nationwide Danish MFS population diagnosed by the Ghent II criteria. In a register-based setting, we identified all Danish patients with MFS (n = 412, men n = 215) by assessment of their medical records. We established a gender and age matched control cohort based on 41,000 control patients (men n = 21,500). MFS cases risk time was 6,669 patient years. We applied Cox regression using each case and his/her control as one stratum, adjusting for age and calendar time. We found a significantly decreased lifespan of 50years compared with 60years among controls. The mortality hazard ratio among MFS compared with controls was significantly increased to3.6 (CI 2.8-4.7, p < 0.001); men 4.0 (CI 2.8-5.7, p < 0.001); women 3.2 (CI 2.1-4.8,p < 0.001). Aorta disease represented the main reason for the overall increased mortality with a hazard ratio of 194.6 (CI 67.4-561.7, p < 0.0001); men 208.7 (CI 53.8-809.1, p < 0.001); women 173.4 (CI 31.5-954.5, p < 0.001). In addition, an unexplained mortality due to respiratory illness was not attributed to pneumothorax. Excluding cardiovascular and respiratory causes of death, we found no indication that MFS is associated with increased mortality for other reasons.