Apart from the degree of mental handicap, the traditional description of a genetic syndrome is limited to somatic characteristics, although occasionally noting some quirk of personality or behaviour. However, these subjective stereotypes become a memorable part of our concept of the syndrome. Although at times startlingly perceptive, more often they are misleading, particularly where there has been only a superficial contact. Latterly more systematic scrutiny, albeit using idiosyncratic rating scales, selected populations, and differing diagnostic standards, has highlighted earlier inadequacies. Consequently the last three years have seen the formation of an informal, multidisciplinary group interested in behavioural phenotypes: an initiative greatly helped by contact with parent groups. Their intention is to develop research and, by introducing some consistency to the observations, to allow comparisons across studies. From this has grown the more public and formal Society for the Study of Behavioural Phenotypes† which was launched at this symposium.