Introduction High rates of sexual partner concurrency have been shown to facilitate the spread of various sexually transmitted infections. Assessments of explicit attitudes to concurrency have however found little difference between populations. We developed a concurrency implicit associations test (C-IAT) to assess if implicit attitudes towards concurrency may vary between individuals and populations and what the correlates of these variations are.

Methods We recruited 869 Belgian (mean age 22.9, SD 5.1) and 70 South African (mean age 22.1, SD 2.5) university students to complete the C-IAT together with a questionnaire concerning sexual behaviour and explicit attitudes to concurrency.

Results The Belgian students C-IATs demonstrated a strong preference for monogamy (−0.78, SD=0.41), with 93.2% of participants having a pro-monogamy C-IAT. The South Africans’ C-IAT demonstrated little preference for concurrency or monogamy (−0.009, SD=0.43), with 34.7% having a pro-monogamy C-IAT (p<0.0001). The South Africans also reported more concurrent sexual behaviour than the Belgians. At a population- but not an individual-level, the C-IAT was a better predictor of actual concurrent behaviour than explicit norms towards concurrency.

Conclusion We found larger differences in implicit than explicit attitudes towards concurrency between populations. These findings need to be replicated in larger samples.