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Neurofibromatosis type 1 (NF1) or von Recklinghausen's disease is one of the most common autosomal dominant inherited diseases in humans with an estimated birth incidence of 1/2500 and a disease prevalence of 1/3000-4000 (1). NF1 gene is located on the pericentromeric region of chromosome 17q11.2 (2). It is a megagene, spaning 350 kb of genomic DNA and consisting of 60 exons encoding an 11-13 kb GTPase activating protein – neurofibromin of 2818 amino acids (3,4). The mutation rate for NF1 gene is high. A half of all NF1 cases are familial, while the other half is caused by a new mutation (5). Genetic molecular testing confirms the disease’s existence but has no predictive value for its severity and course. In the past thirty years, the diagnosis of NF1 was made using a set of clinical criteria developed by the National Institutes of Health Consensus Conference, so called NIH diagnostic criteria (6). The diagnosis of NF1 is based on the presence of two or more of the following: 1) six or more cafe au lait macules, the greatest diameter of which is more than 0.5 cm in prepubertal patients and more than 1.5 cm in postpubertal patients; 2) two or more neurofibromas of any type, or one plexiform neurofibroma; 3) freckling in the axillary or inguinal region; 4) optic glioma; 5) two or more Lisch nodules; 6) a distinctive osseous lesion such as sphenoid dysplasia or pseudarthrosis; 7) a first-degree relative with NF1 according to the preceding criteria. However, the diagnosis cannot always be made in all children using the above mentioned criteria, especially in early childhood when the penetration of NF1 gene in usually not complete (7,8). The cranial magnetic resonance imaging (MRI) is the best method for showing many features of NF1, including optic pathway gliomas, brain tumors of various locations, brain stem tumors, and orbital neurofibromas. Most frequent brain changes in children with NF1 are areas of increased T2-weighted signal intensity – T2-hyperintensities or “unidentified bright objects,” as they usually cannot be visualized using T1-weighted imaging. T2-hyperintensities are age-related findings on MRI and have been observed in 43%-93% of children who suffer from NF1 (9-11). These lesions do not exert mass effect, contrast enhancement, or surrounding edema. They are most commonly found in the basal ganglia, thalamus, cerebellum, and brainstem (12). Former research on multiple T2-hyperintensities on brain MRI in children as diagnostic criterion for NF1 was contradictory and scarce (13-17). The aim of this cross-sectional study was to determine the prevalence, number, and location of multiple (≥2) brain T2-hyperintensities on MRI, and their correlation with age in children with NF1. A further aim was to determine the indicators of diagnostic accuracy of T2-hyperintensities in children of different ages, especially in the early age (from 2 to 7 years) when the NF1 gene penetration is still not completed.