More than 30 war medals have gone missing from the Te Awamutu Museum in Waikato.
The museum realised they were gone only after one of the medals was seen for sale on eBay, prompting an audit of the museum's inventory including 175 historic medals.
Waipa District Council museum and heritage manager Jan White says a police investigation is under way and the museum is trying to recover the medals.
Ms White says their sentimental and historical value is huge.
She says the medals went missing over a 20-year period before the council took over the running of the museum from volunteers in 2005.
The Te Awamutu RSA has bought a South African war medal that was being sold by an American collector on eBay and is returning it to the museum.