Leonard Dunstan walked out of the emergency department of Charing Cross Hospital in Fulham Palace Road just after 5.30pm on Wednesday (February 8).
Temperatures dropped rapidly during the week with the weekend seeing lows of one degree and snow across west London.
Police are concerned as Mr Dunstan has gone missing during the cold spell.
CCTV pictures, released by the Metropolitan Police on Sunday (February 12) show Mr Dunstan leaving the hospital.
He is described as a black man, around 5ft 10ins, medium build with short grey curly hair, balding on top.
When he disappeared Mr Dunstan was wearing a black and white checked shirt and black trousers, and he walks with a sliver stick.
Mr Dunstan is known to spend time in Ealing and Fulham.
Police are concerned because he suffers from dementia and a range of other medical issues.
Anyone with information on his whereabouts is asked to call police via 101 or Missing People on 116000.
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