Considerable differences exist for the spectrum of GJB2 mutations in different populations. Screening for the c.35delG mutation in 256 independent probands, 154 multiplex (familial) and 102 simplex (sporadic), coming from different regions of Turkey revealed 37 (14.5%) homozygotes. The allele frequency of c.35delG ranged from 5% to 53% in different cities. Parental consanguinity was noted in 34% of c.35delG homozygotes, yet it was 55% in c.35delG negatives (p= 0.034). Further screening for GJB2 mutations in multiplex families demonstrated the presence of c.167delT and L90P mutations as well as a novel complex mutation, c.236_ 239delTGCAinsAGATCCG, in single alleles, leading to compound heterozygosity with c.35delG. The homozygous E120del mutation was found in another case. The V27I polymorphism was detected in five alleles, one of which was associated with the E114G change. Assortative mating was a significant factor predicting to detect biallelic mutations in the GJB2 gene. These results confirm the overwhelming majority of c.35delG in the Turkish deaf individuals as well as the presence of other changes detected in Caucasian and Asian populations. c 2003 Wiley-Liss, Inc.