Features of the shell which can be used for aging Roman snails Helix pomatia L. are described. Field evidence suggests that growth breaks in the shell correspond to resting periods during the winter in the juvenile phase of shell growth. The microstructure of the shell is described and the structure of the juvenile breaks and layering in the lip of the adult snail are shown to be similar. It is concluded that the two are analogous, that the layers at the lip are annual, and that it is theoretically possible to trace the adult shell back to the year of hatching. In practice, errors may be made in recording, but the method can be of great value in population studies.