A police force is contacting the relatives of 26 people whose organs and tissue samples were removed and kept without the knowledge of families.
At least 13 samples, taken from post-mortem examinations following unexplained deaths, were found stored at South Tyneside District Hospital.
Northumbria Police said 26 families were being contacted, with Cleveland Police dealing with 13 families.
Both forces admitted samples were kept "longer than necessary".
In a statement, Northumbria Police Temporary Assistant Chief Constable Vanessa Jardine, said: "We understand the gravity of this situation and the devastating affect it has had on the families involved.
"The human tissue samples of cases that happened many years ago have been identified and we have specially trained officers contacting relatives of 26 people to inform them of this.
"It is our priority to make sure this is done as quickly and sympathetically as possible."
The remains were found during an audit at the hospital in March 2015.
South Shields MP Emma Lewell-Buck said: "I think in terms of overall transparency, it's important that the public know the level of numbers involved.
"I'm very disappointed that it's happened in a hospital in my constituency and I think it's such a shame for those families.
"Something like this can just open it up [the grieving process] and it can feel like it just happened the day before all over again."
Sarah Simpson, whose father Terence died in a fall from a roof 22 years ago, said she was "appalled" to be told his tissue samples had been stored.
She said she was now considering legal action.
The Human Tissue Authority (HTA) said that significant improvements had been made to the systems governing the retention of human tissue samples.