In case of total edentulousness the formation of vowels and consonants is impaired, due to the change of the morphology in the oral cavity. The aim of our study was to estimate the influence of the upper complete denture on the phonation of the patient. Patients wearing total upper denture were asked to utter special words with the prosthesis in the mouth and without it, and the change in the formation of "hissing" sounds were noted. The changes in the pronunciation of vowels and consonants were analyzed with the help of a computer program, which provided objective assessment. The data were analyzed statistically. When wearing the prosthesis the scores of the formant became higher and most examined sounds were pronounced faster (p = 0.006). The articulation of patients accustomed to wearing the full total prosthesis was influenced positively by having the prosthesis in the mouth. As a result of these findings it is recommended that the prosthesis be manufactured keeping these phonetic aspects in mind.