• The frequency distribution of major fingerprint patterns (ulnar or radial loops, arches, and whorls) was studied in 47 men with early-onset (aged, ≤64 years), 35 men with late-onset primary degenerative dementia (aged, ≥65 years), and 100 control subjects (aged, 29 to 78 years). Patients with an early, but not those with a late, onset of dementia had significantly more ulnar loops than the control group. This finding, along with other data, is interpreted as indicating that there may be a biologic basis for distinguishing these two forms of dementia.