Almost a third of people living with HIV are unaware they carry the infection, new research has revealed.
Patient campaigners warned that people are still involved in risk-taking behaviour because they do not think they will get HIV.
Barriers to testing for the infection have also led to late detection and have prevented people from benefiting from early treatment, it was claimed.
Dr Jack Lambert, infectious disease consultant at the Mater Hospital, warned a late diagnosis could lead to the rapid onset of Aids.
"We have to continue challenging the stigma that still surrounds HIV in Ireland in order to effect change," said Dr Lambert. "The public needs to know that by avoiding early HIV testing, you put yourself at risk of rapid disease progression - possibly leading to Aids."
A total 6,287 people in Ireland have been diagnosed with HIV since the early 1980s. Latest figures from the Health Protection Surveillance Centre showed 30% of people living with HIV are unaware of their infection.
While the overall diagnosis rate decreased by 3% in 2011, more than half of the 320 people who tested positive presented late with the illness. And 27% of the 85 women newly diagnosed were pregnant.
The highest proportion of new cases was among men who have sex with men (42.5%), while a third were heterosexual men and women, and 5% were injecting drug users. Three mother to child cases were diagnosed.
The figures were released ahead of Irish Aids Day - on Friday June 15 - when a "Don't Guess, Get Tested" campaign will be launched by Open Heart House, the Sexual Health Centre, Aids West, Dublin Aids Alliance and the Red Ribbon Project. Deirdre Seery, chair of HIV Service Network, said healthcare professionals should challenge the stigma surrounding HIV and testing.
"Late presentation of HIV is a significant problem in Ireland and despite attempts to encourage earlier testing for HIV, this situation is of serious concern," Ms Seery said. "In Ireland, as with other countries, there are still many people involved in risk-taking behaviour and because they don't perceive themselves as being at risk of HIV they don't avail of HIV testing."