Background Perceived risk is central to health behaviour theory, though little is known about what creates perceived risk of contracting STDs. We examined self-rated risk of STD in higher sexual risk (HSR) university students in Halifax, Canada, to determine factors associated with recognition of such risk status.

Methods Using an online survey, we asked university students about their perception of their STD risk (greatly/quite a lot at risk versus not very much/no risk), their sexual behaviours, chlamydia knowledge (CK), friends’ more liberal attitudes to sexual risk-taking (FLASRT), depression, and personal factors. HSR was defined as having had both ≥ 2 partners for vaginal sex in the past year and no condom use at last intercourse. Variables initially associated with perceived HSR (p < 0.10) were entered into a logistic regression model controlling for gender to determine which remained associated with perception of being at HSR.

Results The survey response rate was 32% (N = 4490), and 526 were at HSR. Of those with 2–5 partners in the previous year, only 14% rated themselves as at HSR, while 43% of those with ≥ 6 partners did so. In multivariate analysis, compared with those with 2 partners, those with 3 partners and those with 4 were not significantly more likely to perceive themselves at HSR. At 5 partners the Odds Ratio (OR) was 5.30 (95% CI 2.30–12.22) and at ≥ 6 partners it was 9.18; (95% CI 4.42–19.09). FLASRT was also associated with perceived higher risk (OR 1.07; 95% CI 1.02–1.13). CK was not associated with risk perception.

Conclusion Higher risk university students often do not recognise their STD risk status, and more often perceive risk only after a high threshold of multiple partners is reached. Prevention messages should emphasise that STD risk exists at lower levels of multiple partners than students perceive.