Synesthetic phenomenon involves the concomitance of perception of additional sensory characteristics with the normal characteristics of inductive sensory stimulation. This unique sensory phenomenon could affect up to 4% of the general population in various phenomenological forms. It is in the vast majority of developmental cases. There is little known to doctors because synesthetes are usually ignorant or consider their perceptive characteristic as a normal and rightly non-pathological. Knowing synesthesis helps explain it to subjects sometimes diverted to function differently from others. We describe in detail a colour phonema-graph developmental synesthesia, highlighting the complexity of this type of sensoriality, which can sometimes be associated with other positive features such as hypermeasia. The main contributions of research, which have been very rich in the past 20 years, are synthesized in a short review of literature.