A genetic or developmental disorder can be the basis for the failure of a normal dental development, resulting in the absence of 1 or more teeth. For genetic research or the development of a plan of treatment, it is important to determine whether certain patterns of dental agenesis are more common than others. In the present article a new method is described where unique values are assigned to certain patterns of tooth agenesis. Using the idea of binary arithmetic, the absence or presence of teeth are represented by 1 and 0, and translated into corresponding unique values, the 'tooth agenesis code' (TAC). This procedure has advantages over existing methods in that it allows for easier data analysis, can contribute to genetic research into the aetiology of tooth agenesis and enables researchers to communicate unequivocally the phenotypes of their studied case. It can also be used in other areas of oral pathology that require pattern recognition.