Mutations in the cartilage oligomeric matrix protein (COMP) gene are responsible for two dominantly inherited skeletal dysplasias, pseudoachondroplasia (PSACH) and multiple epiphyseal dysplasia (MED). Mutation analysis of the COMP gene in Korean patients with PSACH and MED was performed. All nine patients with PSACH had mutations in the COMP gene, while three of the five patients with MED had detectable COMP mutations. Eight mutations, including three novel mutations, were identified in the COMP gene in the patients with PSACH and MED. Six mutations were found within the calmodulin-like repeats (CLRs) domain, especially in the seventh CLR and the other two mutations were in exon 16 outside of CLRs, which encode the C-terminal globular domain. Among the three novel mutations, two were missense mutations (Asp473Tyr, Asp482His) and one was a consecutive two-codon deletion, delAspAsp(469-473) in the five consecutive aspartic acid residues. All three novel mutations produced the PSACH phenotype.