The Auckland District Health Board is apologising for mistakenly keeping post-mortem tissue samples.
An audit by the board's forensic pathology department picked up that the samples had been retained, even though the coroner had ordered them to be returned to families.
The DHB says the audit found 10 samples were kept, including organ tissue, blood and gastric contents.
It says it happened because the items were stored in various locations and records were kept on multiple databases. Staff resourcing issues were also a factor.
The board says the Chief Coroner was advised last week and his office has contacted the families on Thursday.
It says it must improve its systems to make sure no other families go through this.