Plasma chitotriosidase activity is used for diagnosis and monitoring of Gaucher disease. However, homozygous duplication of a 24 bp region in exon 10 of the chitotriosidase gene (CHIT1) abolishes enzyme activity, limiting its use as a biomarker in Gaucher disease. This study investigates the allele frequency of the 24 bp duplication, in both the general Korean population and in patients with Gaucher disease. Fifteen Korean patients with Gaucher disease and 231 Korean normal individuals were enrolled. Genotyping was performed to identify the 24 bp duplication in exon 10 of CHIT1 using DNA extracted from peripheral leukocytes or dried blood spots. Two patients with Gaucher disease (13.3%) had normal plasma chitotriosidase activity, and carried a homozygous 24 bp duplication of exon 10 of the CHIT1 gene. Nine patients were heterozygote carriers (60.0%). Of the normal 231 Korean individuals, heterozygous duplication was detected in 109 individuals (47.2%) and homozygous duplication in 75 (32.5%). The allele frequency was 56.1% (95% confidence interval, 49.4-62.7%). The frequency of the 24 bp duplication was remarkably high in both Korean patients with Gaucher disease and in the normal population, limiting the efficacy of chitotriosidase as a biomarker in Gaucher disease in Korea. New biomarkers are required that consider the genetic characteristics of different populations.