Mutations in the NF1 gene (17q11.2) cause neurofibromatosis type 1 (NF1), a pleiotropic and progressive autosomal dominant disorder with marked variability of clinical expression. Clinical diagnosis is usually readily achieved in most adult and adolescent patients due to the presence of at least two of the classic signs of NF1. However, the absence of many of the disease-defining features in young children frequently renders definite diagnosis impossible in this age group. Particularly, clinical diagnosis is challenging in young patients whose phenotypical presentation does not lie within the common spectrum of "typical" NF1 features. Sensitive and reliable molecular genetic testing can be of great help in these cases. Here, we report clinical and molecular findings in a 2-year-old boy with features of NF1. Severe growth retardation together with other dysmorphic features was also suggestive for Silver-Russell syndrome (SRS) in this patient. Molecular genetic testing identified a novel NF1 mutation and, thus, enabled a confident NF1 diagnosis despite the unusual phenotypical presentation in this patient.