To compare the demographics and risk factors of men who utilise the services of a municipal public sexually transmitted disease (STD) clinic with those who utilise the services provided by a non-public men's STD clinic operated by a not for profit primary care clinic. A record based review of the characteristics and STD prevalence of men who visited a non-public STD clinic in Baltimore, Maryland, compared with those of a random sample of male attendees of a public STD clinic. Data abstracted from the records included information on age, race/ethnicity, self reported risk behaviours, and STD tests and results. We used chi2 analysis as well as bivariate and multivariate modelling to compare differences in categorical factors between clinics groups. Men who utilised the services at the non-public STD clinic were more often white (71% v 3%, p<0.001), MSM (65% v 2%, p<0.001), and presented for general screening (52% v 15%, p<0.001) compared to those at the public clinic. In addition, they more frequently reported > or =3 partners (22% v 11%, p=0.005), and having an HIV positive partner (10% v 3%, p=0.005). Factors independently associated with attendance at non-public clinic in multivariate analysis were general screening as reason for visit (OR = 11.0, p<0.001), having 3+ partners in past month (OR=10.5, p=0.002), and "sometimes" using condoms (OR=3.6, p=0.033). Non-public STD clinics can reach a distinct segment of the male population with high risk sexual behaviours that might not attend public STD clinics.