BACKGROUND: Multiple endocrine neoplasia type 1 (MEN1) is a familial syndrome characterized by the parathyroid, pancreas and pituitary tumors. Parathyroid tumors are the most common clinical manifestations, occurring in more than 90% of MEN1 patients. Heterozygous germline mutations of the MENIN gene underlie the tumorigenesis in MEN1 and epigenetic alterations along with germline mutations may contribute to tumorigenesis. Here, we investigated the associations between genotype and phenotype in Korean MEN1 patients. METHODS: We analyzed medical records from 14 unrelated MEN1 patients who had newly confirmed MENIN germline mutations, together with 14 previous reports in Korea. Aberrant DNA methylations were also examined in MEN1-related parathyroid tumors using the Infinium HumanMethylation 450 BeadChip. RESULTS: Total 28 germline mutations of MENIN were relatively highly concentrated in exons 7 and 8 compared to previous reports from Western countries. Six mutations (c.111dupT/p.S38Ffs*79, c.225_226insT/p.T76Yfs*41, c.383_398del16/p.S128Tfs*52, c.746dupT/p.H250Afs*20, c.1150G>T/p.E384*, and c.1508G>A/p.G503N) were newly found in the present study. Of interest, four patients (15%) showed unusual initial presentations and three patients were diagnosed incidentally at the general medical checkup. We also found three distinct sites in exon 2 of MENIN were significantly hypomethylated in the MEN1 parathyroid tumors, comparing correspondent blood samples. CONCLUSION: We also have found a lack of genotype/phenotype correlation in Korean MEN1 patients. There were not a few unusual initial manifestations in MEN1 patients, thus, genetic testing for the MENIN germline mutations can provide important information for the better prognosis. Further studies are warranted to investigate altered DNA methylations in the MENIN gene involved in tumorigenesis.