Huntington's disease (HD) arises from an expanded polyglutamine (polyQ) in the N-terminus of the huntingtin (htt) protein. Neuronal degeneration and inclusions containing N-terminal fragments of mutant htt are present in the cortex and striatum of HD brain. Recently, a model of polyQ aggregate structure has been proposed based on studies with synthetic polyQ peptides, and includes an alternating beta-strand/beta-turn structure with seven glutamine residues per beta-strand. We tested this model in the context of the htt exon-1 N-terminal fragment in both mammalian cell culture and in cultured primary cortical neurons. We found our data support this model in the htt protein and provide a better understanding of the structural basis of polyQ aggregation in toxicity in HD.