A new report by the University of Otago says Rugby World Cup fans drank too much and didn't use condoms.
The university and public sexual health clinics found only about one in five fans who had sex during the 2011 tournament used a condom and most had consumed three or more alcoholic drinks.
Jennie Connor, a university professor at Otago who co-authored the study, says one of the major concerns is the increased risk of sexually-transmitted infections.
"People were turning up at sexual health clinics reporting that they'd had sex that was associated in some way with the celebration of the Rugby World Cup, that it almost always involved alcohol, that condom use was fairly low and that those people had a higher rate of infections than the average attender at the clinic."
Professor Connor says the continued promotion of condoms and restricting the availability of alcohol may reduce sexual health risk at future large sporting events.