The analysis indicated that the prevalence of N gonorrhoeae was low with only three cases detected overall (prevalence rate of 0.24 percent). This finding is consistent with previous findings from other settings. The prevalence of C trachomatis, on the other hand, was high, particularly among young, asymptomatic men. The C trachomatis prevalence rate was 9.9 percent among men aged 18 to 25 years, 8.9 percent among woman aged 18 to 25 years, and 3.3 percent among women overall. The high prevalence of C trachomatis at entry to California prisons suggests the need for routine screening at prison entry as well as jail settings where most detainees are incarcerated before entry into the State prison system. The study was part of an ongoing, blinded sentinel surveillance study on the prevalence of HIV, hepatitis, and other STDs in California prisons. The study limited the testing for men to only men aged 25 years or younger while testing was conducted for all women entering the six prisons regardless of age. Standard blood and urine specimens were collected from all participants and leftover urine specimens were saved for the study of disease prevalence in California prisons. Specimens were sent to the Chlamydia Research Laboratory at the University of California, San Francisco for analysis using ligase chain reaction. Statistical analyses were performed using SAS software. Table, references