Huntington's disease is one of the several neurodegenerative diseases caused by dominant mutations that expand the number of glutamine codons within an existing poly‐glutamine (polyQ) repeat sequence of a gene. An expanded polyQ sequence in the huntingtin gene is known to cause the huntingtin protein to aggregate and form intracellular inclusions as disease progresses. However, the role that polyQ‐induced aggregation plays in disease is yet to be fully determined. This review focuses on key questions remaining for how the expanded polyQ sequences affect the aggregation properties of the huntingtin protein and the corresponding effects on cellular machinery. The scope includes the technical challenges that remain for rigorously assessing the effects of aggregation on the cellular machinery. © 2008 IUBMB IUBMB Life, 60(11): 724–728, 2008