Mutations in GJB2 and GJB6 genes are the main causes of autosomal recessive nonsyndromic hearing loss (ARNSHL) in many populations. Here, we investigated GJB2 and GJB6 mutations in 114 patients from 77 affected ARNSHL families including 54 consanguineous marriages and 23 nonrelative marriages in the Iranian population. Clinical studies and genetic counseling were performed for all families. GJB2 and GJB6 genes were directly sequenced. Three known GJB6 large deletions [del(GJB6-D13S1830), del(GJB6-D13S1854), and a 920 kb deletion] were also checked by quantification of a common deleted region within the GJB6 gene. The frequency of consanguinity was 70.13% among the studied families. Biallelic GJB2 mutations were 16.67% in consanguineous marriages and 4.35% in nonrelative marriages. Mutations found were 35delG, delE120, R127H, M163V, W24X, V37I, G12D, V84A, 313-326del14, and E110K. The latter was a novel variant. Neither point mutation nor a large deletion in the GJB6 gene was found in the population. Mean frequency of GJB2 mutations was 17.92%. GJB2 mutations (and not GJB6 mutations) are the major causes of hearing loss in Iran. The role of consanguineous marriages is also highlighted in occurrence of GJB2-related hearing loss. We suggest that other genes may be involved in the population.