Huntington's disease (HD) is a neurological degenerative disorder, inherited by an autosomal dominant mode, and caused by a CAG triplet expansion coding for a poly-glutamine sequence in the huntingtin protein. HD affects 5-10 in 100,000 individuals from Caucasian population. Clinically patients display motor, cognitive and psychological impairment, and death within 10-15 years. Concrete advances have been achieved in the knowledge of the mutational mechanism, alteration of the protein product and their neuropathological effects. A number of tests such as PCR with or without DNA modification, Southern blot and mixed methods are analyzed. We describe their characteristics and effectiveness for the molecular diagnosis of HD.