We report about 52 pediatric patients of 40 different families with confirmed Marfan syndrome (MFS) in 49 patients and Loeys–Dietz syndrome (LDS) in 3 patients. We found 39 different mutations, 15 of them being novel. Phenotype–genotype correlation in the 49 MFS patients showed that the majority of patients carrying mutations in exons 1–21 had ectopic lens (80%). Patients having mutations in exons 23–32 had a higher probability of aortic root dilation, in 50% even above a z score of 3. We found three children with neonatal MFS form, two of them with novel mutations. Of the three LDS patients, only one presented with the typical phenotype of LDS type 1.