Mental health is an essential component of total health, yet psychiatric illness remains surrounded by fear, misunderstanding and stigma in many Nigerian communities. Persons with mental disorders may be hidden, rejected, restrained, taken from one healer to another or brought to professional services only after illness has become severe. Within institutions, psychiatric nursing must move beyond custodial supervision toward purposeful therapeutic care that recognizes the dignity, rights and rehabilitation potential of every patient. This paper examines the changing responsibilities of psychiatric nurses in Nigeria, including therapeutic communication, observation, medication management, family education, rehabilitation, prevention of abuse, community follow-up and mental-health promotion. Particular attention is given to cultural explanations of mental illness, traditional and spiritual healing, substance misuse, suicide risk, the mental-health needs of children and families, and the need to integrate mental-health services into primary health care. The paper argues that every nurse requires basic competence in mental health because psychological distress occurs in all areas of nursing practice. Recommendations are made for education, community services, public education, research and the development of humane, accessible psychiatric care.