Introduction Men-who-have- sex-with-men (MSM) may modify sexual practices to reduce HIV and sexually transmitted infection (STI) risk. HIV pre-exposure prophylaxis (PrEP) may impact risk behaviour and STI acquisition.

Methods We matched HIV-negative MSM attending New York City (NYC) sexual health clinics during 2011–2015 to the NYC HIV registry in 01/2017. We used visit-level data to assess trends in condom use during anal sex (consistent, inconsistent, no use; referent period=3 months), overall and by sexual positioning behaviour. We examined associations between condomless (inconsistent/no use) insertive, condomless receptive, and condomless versatile sex and incident HIV or STI (chlamydia/gonorrhoea/early syphilis). We used regression with generalised estimating equations (referent group=anal sex with condoms), controlling for demographics, partner number, and STI history.

Results The proportion of visits with reported consistent condom use decreased from 2011–2015 (39% to 31%%, p<0.001); inconsistent use increased (48% to 55%%), and no condom use was stable (13%–14%).There were significant declines in consistent condom use across all positioning categories. From all visits, MSM reported positioning as: 19% condomless insertive, 9% condomless receptive, 37% condomless versatile, 35% sex with condoms. For 25,216 STI testing visits that yielded 7438 diagnoses, all condomless-positioning categories were associated with incident STI; highest risk was with condomless insertive sex (aOR 1.8, 95% CI 1.6–1.9). For MSM tested for HIV at 9744 visits, condomless receptive (aOR 2.8; 95% CI 1.9–4.1) and condomless versatile sex (aOR 2.2; 95% CI 1.6–2.8) were associated with incident HIV. Black MSM (~25% of MSM) had the highest risk for STI and HIV (41% of 368 new HIV diagnoses).

Conclusion We documented increases in condomless sex among a sentinel high risk group prior to and during the PrEP era. Insertive sex, perhaps perceived as a safer strategy, was associated with substantial STI risk when condoms were not consistently used. Assuring PrEP access for black MSM is critical.