Police were called to a sudden death of a woman in her 70s at around 4:40pm yesterday at an address on Fosdyke Green in Middlesbrough.
Detectives are treating the death as suspicious, a cordon is in place and forensic officers are on scene.
A man in his 40s from Middlesbrough has been arrested on suspicion of murder and is currently in police custody.
A postmortem is due to take place today to establish how the woman died.
Officers would like to hear from members of the public who may have seen anything suspicious.
Detective Superintendent Rob Donaghy said: “Anyone with information should contact detectives as soon as possible. I want to reassure members of the community that there will be extra patrols in the area.”
Anyone with information should call the non-emergency number 101 or Crimestoppers anonymously on 0800 555 111.