Deafness is a heterogeneous condition with far-reaching effects on social, emotional, and cognitive development. Onset before language has been established happens in about seven per 10,000 people. Increased rates of mental health problems are reported in deaf people. Many regard themselves as members of a cultural minority who use sign language. In this Review, we describe discrepancies between a high burden of common mental health disorders and barriers to health care. About a quarter of deaf individuals have additional disabilities and a high probability of complex mental health needs. Research into factors affecting mental health of deaf children shows that early access to effective communication with family members and peers is desirable. Improved access to health and mental health care can be achieved by provision of specialist services with professionals trained to directly communicate with deaf people and with sign-language interpreters.