"This indicates that for men, sex related to the Rugby World Cup may have been more risky," Wellington Sexual Health clinician Dr Jane Kennedy said.
Most of those who had RWC-related sex had consumed three or more alcoholic drinks.
Study co-author and University of Otago Professor Jennie Connor said that was not surprising given the promotion and availability of alcohol around the event, and New Zealand's drinking culture.
Only about 20 per cent had used a condom.
"This obviously explains a lot of the STI diagnoses in this study and may reflect poor decision-making under the influence of alcohol," said study co-author Dr Jane Morgan of Hamilton Sexual Health clinic.
Four of the 54 (7 per cent) women who had RWC-related sex said it had not been consensual.
The study authors concluded that for future large sporting events, a reduction in the promotion and availability of alcohol as well as the continued promotion of condoms may reduce sexual health and other harm.
People who had RWC-related sex were defined as New Zealanders who had sex related to the RWC or other associated events, New Zealanders whose sexual event leading to the clinic visit was with an overseas visitor primarily in New Zealand for the RWC, and individuals visiting New Zealand primarily for the RWC.
The study appears in the latest issue of the international journal Sexual Health.
