Selected dermatoglyphic variables were analyzed in 50 patients with presumed Alzheimer's disease (AD), 50 patients with dementia referable to other causes, and 100 control patients without known dementia matched for age, sex, and race. AD patients have a significantly increased frequency of ulnar loops on the fingertips, Simian creases on the palms, palmar hypothenar patterns; and large distal loops in the hallucal region. A trend involving an increased frequency of radial loops on the fourth and fifth digits, Sydney lines on the palms, and small distal loops on the soles was also observed. The presence of eight or more ulnar loops or bilateral hypothenar patterns separates AD patients from controls with 84% sensitivity and 63% specificity, supporting the discriminant value of dermatoglyphics in the categorization of patients and in the potential identification of asymptomatic persons at increased risk for AD by dermatoglyphic criteria. The dermatoglyphic patterns observed in the AD patients correspond remarkably with patterns repeatedly observed in Down's syndrome and parents of Down's syndrome children, suggesting that a common genetic factor modulates epidermal ridge formation during fetal development, meiotic non-disjunction during gametogenesis, and accelerated neuronal senescence.