Several reports suggest a genetic relationship between senile dementia of Alzheimer type (SDAT) and Down's syndrome. We have analyzed fingerprints and palmar patterns in an elderly female population comprising a group of 34 patients with probable SDAT, a group of 20 patients with other dementias, and a group of 20 non-demented controls. A bilateral Sydney line was found to be significantly more frequent in the SDAT group than in the two other groups (p less than 0.01, sensitivity 30%, specificity 95%, positive predictive value 91%, negative predictive value 61%). A bilateral Sydney line was as frequent in the SDAT group as in Down's syndrome. The limit value of the index of transversality equal or superior to 31, which is considered as a feature of Down's syndrome, was significantly more frequent in the SDAT group than in the two other groups (right hand p less than 0.05, left hand p less than 0.02). A bilateral discriminant value of this index was also significantly more frequent in the SDAT group than in the two other groups (p less than 0.02), as was an index of transversality higher than 31 on at least one hand (p less than 0.01). In contrast with other reports, we haven't found significantly different frequencies of digital ulnar loops and true hypothenar patterns between the SDAT group and the two others.