Dermatoglyphic alterations may be the result of early prenatal disturbances thought to be implicated in the aetiology of psychiatric illness. In order to test this hypothesis in the particular case of bipolar disorder, we assessed two congenital dermatoglyphic malformations (ridge dissociation (RD) and abnormal features (AF)) and two metric dermatoglyphic traits (total finger ridge count (TFRC) and total a-b ridge count (TABRC)) in a sample of 118 patients with chronic DSM-III-R bipolar illness, and 216 healthy controls. Bipolar cases showed a significant excess of RD and AF (OR = 2.80; 95% CI: 2.31-3.38) when compared with controls. In the cases, the presence of anomalies was associated with earlier age of onset. No differences were found for TFRC and TABRC. No associations were found with sex or familial morbid risk of psychiatric disorders. Our findings add further weight to the suggestion that early developmental disruption is a risk factor for later bipolar disorder.