This study examines the requirement for testing patients for other sexually transmitted infections (STIs) and bacterial vaginosis (BV) when diagnosed with genital chlamydia during opportunistic screening. Data were collected on all patients participating in the Department of Health chlamydia screening pilot study in Portsmouth. One thousand two hundred and forty-five women and 490 men with genital chlamydia were seen in Portsmouth genitourinary medicine (GUM) department. Of the women screened in GUM, 28% had coexisting STIs and 21% had BV. The corresponding figures for those initially screened in the community were 4% and 17%. An increased number of female sexual partners of male patients (76%) and male partners of female patients (55%) of the GUM group had co-infections; 58% of male partners from the community group had another STI. The increased morbidity associated with these infections warrants screening of all patients with chlamydia for other STIs and BV.