Officers are appealing for help to trace the whereabouts of 72-year-old Don Allen from Portsmouth.
Mr Allen was last seen at his home in Hale Court, Fratton Road, at around 1.45pm today.
Hampshire Constabulary says its officers are becoming increasingly concerned about him as he suffers from Alzheimer’s and diabetes.
He is white, about 5ft 6ins tall, and wears glasses.
He was last seen wearing trousers, a short-sleeved shirt and slippers.
If you have seen him today or know where he might be, please call officers at Cosham police station on 101.
Alternatively call Crimestoppers on 0800 555 111, where information can be left anonymously.