Adult-onset hearing loss is very common but we know little about the underlying molecular pathogenesis, impeding development of therapies. We took a genetic approach to identify new molecules involved in hearing loss by screening a large cohort of newly-generated mouse mutants using a sensitive electrophysiological test, the auditory brainstem response. We review here the findings from this screen. Thirty-eight unexpected genes associated with raised thresholds were detected from our unbiased sample of 1,211 genes tested, suggesting extreme genetic heterogeneity. A wide range of auditory pathophysiologies was found, and some mutant lines showed normal development followed by deterioration of responses, revealing new molecular pathways involved in progressive hearing loss. Several of the genes were associated with the range of hearing thresholds in the human population and one, SPNS2, was involved in childhood deafness. The new pathways required for maintenance of hearing discovered by this screen present new therapeutic opportunities.