A habit is a routine of behavior that is repeated regularly and tends to occur unconsciously. Habits are one of the major etiologic factors which will leads to malformation in dento-facial structures. They are the most frequent cause of these malformations mostly seen in the early childhood and mixed dentition stages. Bad oral habits extended over a long period could cause damage to the dento-skeletal development. The most common are sucking the thumb (or another finger), lips or objects, as well as atypical swallowing and oral breathing. Tongue thrust is another bad oral habit where the interposition of the tongue between the dental arches can be observed. At the same time, a low activity of the elevator muscles of the mandible in contrast to a high activity of the perioral muscles, in particular of the mental muscle, can be observed.The diagnosis should be made as soon as possible as, if not treated early, severe malocclusions can result.