Objectives Decisions to use condoms are made within partnerships. We examined the associations between inconsistent or no condom use and individual and partnership characteristics. We also examined the relative importance of individual versus partnership factors.

Methods Cross-sectional study of heterosexual individuals enrolled from the sexually transmitted infections (STI) outpatient clinic in Amsterdam, the Netherlands, from May to August 2010. Participants completed a questionnaire about sexual behaviour with the last four partners in the preceding year. Participant and partnership factors associated with inconsistent or no condom use in steady and casual partnerships were identified.

Results 2144 individuals were included, reporting 6401 partnerships; 54.7% were female, the median age was 25 (IQR 22–30) years and 79.9% were Dutch. Inconsistent or no condom use occurred in 86.1% of 2387 steady partnerships and in 66.5% of 4014 casual partnerships. There was statistical evidence of associations between inconsistent condom use in steady partnerships and ethnic concordance, longer duration, higher number of sex acts, practising anal sex, and sex-related drug use. In casual partnerships, associations were found with having an older partner, ethnic concordance, longer duration, higher number of sex acts, anal sex, sex-related drug use, ongoing partnerships and concurrency. In multivariable models, partnership factors explained 50.9% of the variance in steady partnerships and 70.1% in casual partnerships compared with 10.5% and 15.4% respectively for individual factors.

Conclusions Among heterosexual STI clinic attendees in Amsterdam, partnership factors are more important factors related with inconsistent condom use than characteristics of the individual.