Background: The aim of this study was to determine the reorganization of the language areas in patients with tumors located near speech centers using functional magnetic resonance imaging (fMRI). Material/Methods: fMRI was performed prior to the surgical treatment of 11 right-handed patients with tumors located close to the Broca's or Wernicke's areas of the left hemisphere. The analysis included a record of the activity in four regions of interest (ROIs): Broca's and Wernicke's areas, and their anatomic homologues in the right hemisphere. For each patient a regional lateralization index was calculated separately for Broca's area versus its right-hemisphere homolog and Wernicke's area versus its right-hemisphere homolog. The results were correlated with the histopathological type of the tumor and its size. Results: Our fMRI examinations showed activation of the Broca's area in the right hemisphere in 3/4 cases of low grade gliomas (LGG) localized in the left frontal lobe. In one case of the high grade glioma (HGG) only the left hemisphere Broca's area was activated (LI=1). Activation in Wernicke's area in both hemispheres was obtained irrespective of the size and histological type of the tumor. All tumors localized in the left temporal lobe were HGG. We obtained activation only in the right hemisphere Wernicke's area in 4/5 of the cases. In 4/5 of the cases activation in Broca's area was present- in 2 cases in the left hemisphere, in 1 case in the right hemisphere and in 1 case bilateral. Conclusions: The presence of a neoplastic lesion in close topographic relationship to language areas induces their functional reorganization. fMRI is an useful method for determination of language areas localization in pre-operative planning. HGG tumors localized near Wernicke's area lead to transfer its function to the healthy hemisphere and/or to decreased activity in the affected hemisphere.