Objective: To estimate the predictive values for HIV infection of diag
nosis of oral manifestations of the infection. Method: Prevalence of o
ral manifestations was compared in cross sectional blinded clinical ex
aminations of homosexual men attending a genitourinary medicine clinic
. Data were extrapolated to populations in England and Wales based on
estimates of the prevalence of HIV infection. Results: Data were analy
sed for 572 HIV infected and non-infected men (312 and 260 respectivel
y). Positive predictive values for erythematous candidiasis, hairy leu
coplakia and pseudomembranous candidiasis were greater than 0.96 at th
e genitourinary medicine clinic and are estimated to be greater than 0
.72 among homosexual men in London. Conclusions: Clinical diagnoses of
mucosal lesions alone are poor predictors of HIV infection but are us
eful when used in conjunction with a social history to establish if th
ere are risk factors for infection.