Comprehensive analysis using a large number of unbiased (social health insurance-based) samples has clarified the genetic epidemiology of hearing loss. The overall diagnosis rate is approximately 40%, with the rate varying for each age category. GJB2 is the most prevalent causative gene in Japanese hearing loss patients, and the major (commonly found) gene variants (such as variants in CDH23, SLC26A4, STRC) cause deafness in 30–40% of cases. The remaining cases of hearing loss are the result of various rare gene variants (total 51 genes). The diagnostic rate differs for each age group; approximately 50% in the pre-lingual onset group, about 30% for the juvenile/young adult-onset group, and about 20% for those with onset after 40 years of age. Interestingly, each group showed a different kind of causative gene. The diagnostic rate for the pre-lingual onset group (congenital group) was also supported by a recent large-scale comprehensive etiological study based on the newborn hearing screening program for 153,913 infants. A review of papers that performed next-generation sequencing analysis showed that variants in GJB2 are predominant across all ethnic groups, and several causative genes, including SLC26A4, MYO15A, MYO7A, and CDH23, are also frequently found across diverse populations. It was revealed that similar deafness genes (but distinct mutational spectra) are involved in hearing loss patients regardless of ethnicity. These ethnic distinctions are most likely the result of founder mutations that occurred during human migration.