Hackers have targeted the system at Tullamore's Midlands Regional Hospital, HSE confirmed.
Hospitals were attacked with ransomware, which is software that requires ransom to be paid in return for access to files and devices.
In a statement, HSE confirmed that the Laboratory Information System (LIS) at the hospital was targeted.
They say that there is no evidence that malicious software has spread to other systems in broader health services.
Operations are currently underway to ensure that the affected system is safely brought back online.
As a precautionary measure, the Data Protection Commission has been contacted and notified of the incident.
It is not immediately clear whether patient information is affected in ransomware attacks.
A spokesperson for HSE said: & # 39; There is no evidence of transmission in wider health services outside the initial attack.
"There is no impact on patient care and the business continuity plan operates until the full system is restored."