Finger ridge counts (FRC) based on the dermal ridges of the human fingerprint are known to be asymmetrical with the majority of individuals having more ridges on the right hand (R >) while a minority have more on the left (L >). Using 48 adult participants, we investigated the association between sex, FRC asymmetry and performance on a battery of six cognitive tasks (two female-favouring, two male-favouring and two sex-neutral). Sex differences in task performance were in the predicted direction although the size of the difference was task dependent. The major finding was an association between FRC asymmetry and task performance. Irrespective of sex, female-favouring tasks were performed better by L > individuals, male-favouring tasks were performed better by R > individuals, while sex-neutral tasks showed no group differences. These FRC-related differences in cognitive performance, that are present within each sex, could contribute to the elusive nature of sex differences in cognitive abilities. In addition, given that finger ridge development is complete by the 16th foetal week, the relationship between FRC asymmetry and pattern of cognitive performance that we have found is consistent with the view that prenatal biological factors, possibly gonadal steroids, exert an organizing influence on neuropsychological development. (C) 2001 Elsevier Science Ltd. All rights reserved.