Clinical and neuropathologic findings from a Danish family in which a dementing illness is segregating as an apparent autosomal dominant disorder were previously described (Gydesen et al. 1987). We present here genetic findings from this family in which linkage analysis has excluded Huntington's disease and chromosome 21-encoded Alzheimer's disease. None of the known prion mutations has been detected in affected individuals from this family. However, linkage analysis with the prion gene has been uninformative. This family probably represents a novel genetic dementia.