Hearing impairment (HI) in children with a congenital or early onset is explained by genetic and environmental factors. Genetic factors are regarded as responsible for more than half of the cases of congenital HI and environmental factors are responsible for another 14-30%, but the etiology is still unknown in 20-40% [1]. Regarding the genetic causes, 30% are considered syndrome related, whereas 70% non-syndromic. Congenital infections and neonatal trauma may explain 20-30%. Without a well-run vaccination program, congenital rubella syndrome remains the most important cause of acquired infectious congenital HI, whereas in more developed areas, congenital cytomegalovirus (cCMV) has become the most common intrauterine infection. cCMV may cause 20% of congenital HI, but it is also responsible for late onset and progressive HI. Development, including advanced MRI, cellular biology and genetic analysis has within a few years provided diagnostic advancements in the etiology of HI.