As part of the International Sexuality Description Project, 16 362 participants from 52 nations responded to measures of the Big Five and ‘risky’ sexuality. It was expected that low levels of agreeableness and conscientiousness would be universally associated with relationship infidelity. Sexual promiscuity, in contrast, was expected to positively relate to extraversion and neuroticism. Analyses across 10 world regions revealed relationship infidelity was universally associated with low agreeableness and low conscientiousness. Sexual promiscuity was somewhat related to these traits as well, but was more highly related to extraversion across many, but not all, world regions. Both forms of risky sexual behaviour were generally unrelated to neuroticism and openness across cultures. Discussion focuses on possible explanations of regional differences in personality–sexuality linkages. Copyright © 2004 John Wiley & Sons, Ltd.