Objective To study the prevalence of skin positivity to purified protein derivative (PPD) in human immunodeficiency virus (HIV) infected patients in Hong Kong Methods Consecutive clients of an HIV clinic were administered the PPD test and 2 units of PPD RT23 were used The area of induration was then measured in 48 to 72 h Results were related to patient characteristics and HIV related parameters Results Eight (17 0%) out of 47 clients tested positive to the administration of 2 units of PPD RT23 If the cutoff were raised to 10 mm according to current practice, only two (4 3%) would test positive Conclusion The prevalence of PPD positivity in HIV infected patients in Hong Kong is 17%, when a cutoff of 5 mm is used This figure may form the basis for further studies on the utility of isoniazid preventive therapy in this group of patients Objective To study the prevalence of skin positivity to purified protein derivative (PPD) in human immunodeficiency virus (HIV) infected patients in Hong Kong Methods Consecutive clients of an HIV clinic were administered the PPD test and 2 units of PPD RT23 were used The area of induration was then measured in 48 to 72 h Results were related to patient characteristics and HIV related parameters Results Eight (17 0%) out of 47 clients tested positive to the administration of 2 units of PPD RT23 If the cutoff were raised to 10 mm according to current practice, only two (43%) would test positive Conclusion The prevalence of PPD positivity in HIV infected patients in Hong Kong is 17%, when a cutoff of 5 mm is used This figure may form the basis for further studies on the utility of isoniazid preventive therapy in this group of patients