Huntington's disease (HD) is an inherited autosomal dominant, neurodegenerative disease that is caused by a gain of function mutation characterized by the expansion of a CAG trinucleotide repeat in exon 1 of the huntingtin (htt) gene. Since hairpin small interference RNA (shRNA) technology allows inhibition of specific gene expression in vitro and in vivo, vector-mediated expression of an shRNA directed to htt mRNA could form the basis of a new treatment modality for HD. By initial plasmid transfection of 293 cells, we identified one exon 1-targeted shRNA, which efficiently inhibited expression of an htt exon 1-GFP fusion protein and the endogenous htt gene. A replication-deficient adenovirus (Ad) vector Adie-1-1 was constructed to express this shRNA from the U6 promoter. In A549 cells expressing exon 1 of htt with an expanded CAG allele, Adie- 1-1 efficiently prevented htt exon 1 expression and htt aggregate formation. In addition, in different neuronal and nonneuronal cell lines, Adie-1-1 efficiently inhibited the expression of endogenous htt. Together, this data indicates the delineation of an shRNA strategy that may become the basis for treatment of HD.