Background and Objectives There is marked underdiagnosis of genital chlamydial infection in Victoria, Australia, and little is known about the diagnostic or treatment practices of general practitioners (GPs) for this condition. Such information is required to develop more effective epidemiologic surveillance and control of this disease in Australia. Goal of this Study To measure indicators of knowledge and practices of GPs in Melbourne in relation to their diagnosis and management of genital chlamydial infection. Study Design A self-administered questionnaire delivered by mail to a random sample of 327 Melbourne GPs. Results The response rate was 83%. Female doctors were significantly more likely to test symptomatic patients and to screen asymptomatic patients than were male doctors. Having a large proportion of patients in the high-risk age groups was not a reliable predictor of diagnostic practices. Only 49% of respondents knew how to correctly take specimens for diagnosis of chlamydial infection, and only 41% knew the disease is notifiable. Conclusion Underdiagnosis of chlamydia is due partially to general practitioners having a low level of suspicion of the disease in their patients and to inappropriate specimen collection technique. The present system of chlamydia surveillance is inadequately measuring disease trends, and the information from this survey should be useful in the development of medical training programs.