Rett syndrome (RTT) is an X-linked disorder caused by mutations in the methyl-CpG-binding protein 2 gene (MECP2). The incidence is 1:10,000-1:15,000 females worldwide. To date, the mutational spectrum of MECP2 in the Ukrainian population is not known. Here we present first Ukrainian girl with classic clinical signs of RTT, in whom mutation of MECP2 gene was detected. Total genomic DNA was extracted from a dry blood spot using the QIAamp DNA Mini Kit (Qiagen) according to the manufacturer's protocol. Genomic DNA was used to amplify coding sequence and exon/intron borders of MECP2 gene. Products were examined by restriction analysis and automatic direct sequencing. The sequencing analysis of our patient revealed a small deletion of 4 bases AAAG at position 856-859 in exon 4 of MECP2 gene (856-859del4). This mutation leads to a frameshift (K286fs) and a premature stop codon. The creation of premature stop codon results in synthesis of truncated MeCP2 protein. Localization of the mutation into the transcription repression domain (TRD) probably affects the function of MECP2 protein in the process of transcriptional repression. To our knowledge this is the first case from Ukraine, in whom clinical diagnosis of RTT was confirmed by mutation analysis of MECP2 gene. Mutation analyses of further patients are needed to establish the spectrum of MECP2 mutations in the Ukrainian population. (Tab. 1, Fig. 3, Ref. 22.)