The aim of the study was to examine the position and function of the tongue in cleft lip and palate (CLP) patients and to reveal their impact on alveolar bone development. Two hundred and fifty-eight CLP children and 50 healthy children as control group were included in the study. Tongue function and position were assessed by ultrasound examination. In CLP patients the dorsum of the tongue was deformed and the asymmetry of some tongue structures was also found out (mainly the massive of the tongue muscles). Low tip and high dorsum position were specific for CLP children as well as discoordinated tongue movements. Both in static and dynamic condition the tongue was pressed to the lower alveolar bone thus disturbing its development. The obtained data showed tongue position and function to be one of the causes for lower promacrognathy and lingual inclination of incisors in CLP patients. The absence of tongue impact on the upper alveolar bone should be seen as one of the factors for upper retromicrognathy.