A Brazilian man has been arrested on suspicion of keeping his wife locked in a cellar for at least eight years while he lived upstairs with another woman.
Acting on a tip, police found 64-year-old Sebastiana Aparecida Groppo lying naked in a filthy basement in the city of Sorocaba in Sao Paulo state.
Her husband Joao Batista Groppo told officers he had locked her up because she was mentally ill and aggressive.
Police said Mrs Groppo appeared to be in good physical health.
But they said she showed signs of mental problems that could have been caused by her confinement.
Police inspector Jaqueline Barcelos Coutinho told the Associated Press news agency she was shocked when she arrived at Mr Groppo's house and found Mrs Groppo behind a padlocked iron gate in the cellar.
"She was lying nude on a concrete bed inside a foul-smelling, humid cubicle with no electricity or ventilation," Ms Coutinho said.
"She was in a degrading situation unfit for animals".
Mr Groppo, 64, initially said he had kept his wife confined for 16 years but then revised the time to eight, Ms Coutinho said.
"He told us that locking her up was the only way he could think of to prevent her from wandering off and getting lost," she added.
The couple have been married for more than 40 years.
Mrs Groppo was treated in hospital and then taken to the house of her son in a nearby city.
Mr Groppo and the other woman he lives with are facing charges of false imprisonment.