The numbers of patients with chronic prostatitis are increasing in all countries. The aim of this study was to determine the prevalence of chlamydia in patients with non-bacterial prostatitis. Fifty-five patients suffering with back pain, discomfort on voiding and ejaculation and perineal ache, and 35 normal patients, were examined between December 1995 and July 1997. Urine samples and prostatic secretions after prostate massage were collected from all patients. Chlamydia antigens were tested for with Chlamyphast. Chlamydia antigen was positive in 14 of the 55 (25.4%) patients with non-bacterial prostatitis, but positive in only 2 (6%) patients in the control group. The difference between the two groups was statistically significant (p=0.0268), After treatment with doxycycline 100 mg twice daily for 10 days, the clinic cure rate was 80%.