Huntington's disease is an autosomal dominant neurodegenerative disease that leads to characteristic clinical symptoms that manifest as chorea, psychiatric impairment, cognitive decline and dementia. The disease is caused by an increased number of CAG trinucleotide repeats on chromosome 4 (4p16.3) that encodes protein huntingtin (HTT). The selective therapy for Huntington's disease is still non-existent. Current therapy is symptomatic treatment where the dopamine blockers have turned out to be the most useful. The aim of the study has been to determine the frequency and the extension of CAG trinucleotide repeats in individuals suspected of having Huntington's disease (HD) whose blood samples were tested in UHC Zagreb in time period from January 2003 to July 2012. The data for this study has been gathered from medical documentation and analysed by descriptive statistics. Through the analysis of 486 blood samples by gel electrophoresis, the normal amount of CAG trinucleotide repeats (≤ 26 ) was found in 303 samples (62%), the intermediate number of CAG trinucleotide repeats (27-35) was found in 24 samples (5%), and the increased number CAG trinucleotide repeats was found to be present in 159 samples (33%).