The number of gay men in the North diagnosed with HIV has hit a record high.
The total of new HIV cases in the North rose by a fifth last year and 53 involved homosexual men, a report for the Public Health Agency said.
That is the largest annual number for gay men recorded in the North and most cases were acquired in the UK.
Agency consultant in health protection Dr Neil Irvine said: "The safer sex message of the 1980s has been forgotten. Maybe people perceive themselves to be less at risk but that is part of a picture that has been seen across western Europe and most of North America."
The number of new HIV diagnoses in the North rose by 20% to 79 last year.
There are 474 people living with HIV in the North, an increase of 12% on 2009.
HIV is transmitted through contact with bodily fluids like blood. In the North, most transmission occurs through unprotected sex with an infected person. It can also be transmitted by sharing contaminated needles.
The report, HIV And STI Surveillance In Northern Ireland 2011, said new STI (sexually transmitted infection) diagnoses increased by 6% on 2009.
Other findings included:
* Uncomplicated gonorrhoea increased by 13%;
* Genital herpes simplex (first episode) increased by 18%;
* Genital warts (first episode) increased by 2%;
* Non-specific genital infection increased by 14%.
Dr Irvine said: "We want to take the opportunity presented by World Aids Day to raise awareness about HIV and STIs.
"While young people and MSM (men who have sex with men) are particularly at risk, the safer sex message applies to everyone. We know people may be infected with HIV and STIs without having any symptoms, so it is important to protect yourself and to stop the spread of infection to others.
"Use condoms, limit the number of your sexual partners, and get checked at your GP surgery or your local genito urinary medicine clinic if you have put yourself at risk."