Ultraconserved regions (UCRs) are defined as DNA sequences, which are absolutely conserved between orthologous genomic regions of multiple species. However, recent studies have proved the presence of polymorphisms within UCRs. Most of the UCRs have not yet been functionally annotated, therefore their effect on phenotype and involvement in disease development remain substantially unknown. The aims of the thesis were to: 1. remap previously reported UCRs according to the latest human genome release using bioinformatics tools, 2. identify genes overlapping UCRs, 3. identify polymorphisms within UCRs and 4. check whether any associations between UCR polymorphisms and phenotype/diseases exist. Using BioMart data mining tool we showed that 25 % of UCRs are intergenic, while the rest overlap genes. Our analysis performed by BioMart identified 30,139 polymorphisms within UCRs. Among these, 183 have been annotated to be associated with phenotype according to the Ensembl genome browser. For 37 among 183 polymorphisms it was possible to obtain published literature reporting associations with phenotype. Polymorphisms are associated with various diseases, for example with familial adenomatous polyposis, adolescent idiopathic scoliosis, amyotrophic lateral sclerosis, muscle dystrophies and spastic paraplegia. Our results serve as a basis for further investigation of UCRs’ functions and identification of important regions within these segments.