We have reviewed differential diagnostics and treatment of mental disorders with delusions in elderly people. Their delusions are often influenced by sensory disturbances, general medical conditions, and psychological as well as living status. Because delusions are not specific to particular disorders, differential diagnostics require assessment of other symptoms. In making a treatment plan, it is essential to consider psychosocial factors that contribute to development of delusions. The goal should be to help the patient live an ordinary life even if their delusions persist.