An analysis of palmar crease variants was carried out in a group of "at risk" newborns, without any evident congenital anomalies. This group consisted of 108 prematures, 74 infants who were small for gestational age, 62 newborns with history of gestational complications, and 46 newborns with a history of intrauterine methadone exposure. A system of classification was developed based on observations of 500 normal newborns as control subjects, 466 normal mothers, and 200 normal children. The palmar crease variants can be divided into four main groups, schematically presented as normal variants, simian crease and its variants, Sydney line and its variants, and another group of unusual variants which do not fit into the other groups. A study of these groups revealed that familial components, race, sex, and age are factors that can influence the expression of palmar crease patterns. There is an increased frequency of abnormal creases in each of the groups of "at risk" newborns. Moreover, there is an apparent association of interrupted transrerse creases and intrauterine methadone exposure.