OBJECTIVES: To determine the level of awareness of genital chlamydial infection, and level of knowledge related to this infection, in genitourinary medicine (GUM) clinic attenders. METHODS: 500 consecutive patients attending a GUM clinic for the first time during a 3 month study period were invited to complete an anonymous self administered questionnaire on aspects of chlamydial infection. RESULTS: 482 (96.4%) questionnaires were available for analysis (57% female). 289 (60%) respondents had heard of Chlamydia trachomatis compared with 472 (98%) for thrush, 467 (97%) for HIV/AIDS, and 434 (90%) for gonorrhoea. Subjective knowledge of chlamydia, relative to the other infections, was poor. Overall, the mean chlamydial knowledge score was 0.38 (range 0.0-1.0). Females scored significantly higher than males (0.45 v 0.26; p < 0.00001) and younger females scored significantly higher than older females (p = 0.001). More females had experienced genital chlamydial infection than males (22.4% v 12.1%, p = 0.004). Those with prior exposure to C trachomatis had higher mean knowledge scores than those without (males 0.55 v 0.25, p < 0.00001; females 0.68 v 0.37, p < 0.00001). CONCLUSION: Even for a population considered as "high risk" by their attendance at a GUM clinic, there was poor awareness of genital chlamydial infection, and mean knowledge scores were low. Whether increased knowledge was due to successful health education at the time of diagnosis in those with previous infection remains to be determined. In the future, one would hope for increased knowledge scores in those at risk before the acquisition of infection, which may be achieved by national health education programmes for C trachomatis.