There was a 33% increase in the number of people who tested positive for HIV in Ireland last year.
The HSE reported 498 notifications of the virus, compared to 377 in 2014.
The figures have been released by the Health Protection Surveillance Centre and may be subject to change as more detailed information becomes available later this year.
The significant increase in HIV cases is partly due to an outbreak of HIV among people who inject drugs in Dublin.
There was also a change to the notification procedure for HIV, leading to earlier and more complete notification of all new cases.
The HSE, however, are concerned about an increase in the number of cases identified so far that have occurred among men who have sex with men.
In response, a national multi-disciplinary response group has been established to investigate this increase.
It will also seek to establish the extent and causes for the increase, and to plan appropriate interventions and communications to prevent the spread of HIV and STIs.
Resources for men who have sex with men are available at www.man2man.ie, a partnership initiative by HSE and the Gay Health Network.