A new approach based on the study of distortion in the AO3 layer of ABO3 perovskites is proposed with the aim to discuss their ferroelectric properties. Rhombohedral distortions exist for either A-O average distances shorter than 2.7 A (space group Nr.161) or A-O distances larger than 3 Å (space group Nr.160). In the case of small distortions tetragonal or orthorhombic symmetries are preferred. Moreover, a relationship between the dimension of the B cation and the distortion in this type of structure has been established. Preliminary results show interesting correlations between distortions in the AO3 plane and the critical temperature of ferroelectric materials.