Chlamydia is currently the most frequently notified infectious disease in New South Wales (NSW). Published articles relating to chlamydia prevalence in Australian prison settings are sparse, but studies from the United Kingdom and the United States indicate relatively high chlamydia prevalence among young incarcerated individuals. This article reports on findings from an enhanced chlamydia surveillance programme in NSW prisons between 2005 and 2007. The authors report a relatively low chlamydia prevalence among the general population of NSW prisoners (compared with figures from the United Kingdom and United States), which by the end of 2007 was 4%. The average crude chlamydia notification rate for the NSW prison population during the review period was about four times that of the general NSW community - 716/100,000 during the review period compared with 175/100,000 in the NSW general community. The average crude chlamydia notification rate for Aboriginal prisoners during the review period was 1262/100,000, compared with 1470/100,000 in the general Australian Aboriginal population. The authors grapple with the dilemma of expanding chlamydia screening and treatment services for the sexual health benefits of prison populations with static prison health budgets on one hand, and limited evidence of cost-effectiveness of such an expensive intervention on the other.