Gardaí and the Data Protection Commissioner are investigating how private information on Tallaght Hospital patients was compromised.
The hospital has described the breach as unauthorised access and disclosure of patient information.
Tallaght Hospital had been using Uscribe, based in the Phillipines, to transcribe medical records. An evaluation of the service revealed some dictated letters did not come back transcribed.
That contract was terminated in May and the hospital employed a new service provider, implementing new policies and procedures.
"Tallaght Hospital has asked the Garda Síochána to assist it in determining how sensitive patient information got into inappropriate hands," John O’Connell Acting Chief Executive of Tallaght Hospital said.
"It is now evident that information has been subject to unauthorised access and disclosure. The hospital has been working closely with the National Bureau of Investigations in the Philippines and the UK Information Commissioner."
O’Connell added the hospital is determined to resolve the matter thoroughly and as quickly as possible, and the hospital board, as well as the HSE, have been informed of the events.