East Midlands Ambulance Service has apologised after losing 42,000 electronic copies of patient report forms.
The data cartridge contained the scanned handwritten forms, which are from September 2012 to November 2012.
The cartridge was lost from the service’s divisional headquarters in Beechdale, Nottingham.
EMAS chief executive Sye Noyes said: “We take our responsibility for the security and confidentiality of the information we record and store very seriously, and express sincere apologies for a patient data loss incident which we have reported to the Information Commissioner this week.
“The cartridge is small (see photograph) and there is a possibility that it is still on our premises; we are conducting a thorough search of the building.”
She said it was unlikely the information could be viewed by anyone outside EMAS as it can only be read via specific hardware, which is no longer in production.