Sexually transmitted diseases (STDs) are known to exist in wild and domesticated animals, but little is know about behavioural defences that animals use to reduce the risk of acquiring STDs. Using comparative data and a phylogeny of primates, I investigated whether behaviours hypothesized to reduce STD transmission are correlated with measures of STD risk involving mating promiscuity and life-history traits. Comparative tests revealed no support for genital inspection as a means to identify and avoid infected individuals with genital inspection was performed more commonly by males than females and uncorrelated with mating promiscuity. Primate species characterized by increased promiscuity were not more likely to display genital self-grooming following mating. Similarly, males and females of these species were not more likely to urinate immediately after mating, counter to suggestions that urination flushes microorganisms from the urethra and surrounding genital areas. Finally, monogamy was not correlated with a slow life history, which differs from predictions that monogamy is a response to increased STD risk in long-lived animals. Tests involving monogamy remained unsupported after controlling for potentially confounding variables, and all tests yielded similar results in phylogenetic and nonphylogenetic tests. Few results were significant even before controlling statistically for multiple comparisons, but nonsignificance was unlikely due to low statistical power or poor data quality in all tests. Instead, the comparative patterns were consistent with theoretical models showing that precopulatory behavioural defences to STDs, such as mate choice, are unlikely to be fully effective. In addition, many putative behavioural defences to STDs in primates entail substantial fitness costs in terms of reproductive output, offspring quality and infanticide avoidance. Copyright 2003 Published by Elsevier Ltd on behalf of The Association for the Study of Animal Behaviour.