This paper investigates the change in symptomatology that occurs as specific ego functions, related to psychoanalytic symbol formation, mature and develop during the first half of the third year of life. The manifestations of acute emotional disturbance before this time are anxiety, somatic symptoms, and sleep disturbances. After this time there may be added fantasy-determined symptoms such as phobias. This transition and its timing is illustrated through a case presentation and supported by clinical descriptions found in the literature. The symbolizing function does not arise de novo but is the complex end product of a series of developments. The series of steps is outlined in relation to Piaget's exploration of the appearance of symbols in childhood. Before the third year of life symbols occur which are of the conscious metaphorical and generic type, such as flags representing a nation. During the first half of the third year of life symbols with unconscious meanings appear, and the child becomes capable of producing true phobias.