Background Identification of STI risk groups is essential for optimal prevention and medical care. Until now, swingers-that is, heterosexual couples who are practising mate swapping, group sex, visit sex clubs for couples, are not considered as a specific risk group for STI in healthcare services and prevention. Objective To compare STI prevalence rates in swingers with that in other risk groups. Methods At the STI clinic, South Limburg, The Netherlands, whether an attendee is a swinger has been systematically registered since 2007. STI clinic surveillance data were analysed to assess the swingers' share of consultations and STI diagnoses-here Chlamydia trachomatis (CT) and/or Neisseria gonorrhoea (NG). Results Of 8971 consultations, 12% comprised swingers (median age 43 years, IQR 38-48). Overall, STI prevalence was highest in youth, men who have sex with men (MSM) and swingers. Older swingers had a CT prevalence of 10% and an NG prevalence of 4%. The share in STI diagnoses in the older age group (>45 years) comprised 55% for swingers and 31% for MSM. Conclusions Swingers comprise a substantial proportion of STI consultations. They are a mainly older age group and form an important part of STI diagnoses. While other risk groups for STI, such as young heterosexuals and MSM, are systematically identified at STI healthcare facilities and provided with appropriate services, this is generally not the case for swingers. Swingers, like other groups with risk behaviours, need to be identified and treated as a risk group in STI prevention and care.