The scope of this study was to describe knowledge of military conscripts about STD in relation to level of schooling upon enlistment in the Brazilian Army. A self-administered questionnaire with demographic and clinical aspects, forms of transmission, sexual behavior and access to STD information was applied in a national sample in 2007. Variables associated with low schooling were: being 19-20 years old [OR=1.2(95%CI:1.18-1.32)]; saying that STD can be transmitted by: eating contaminated food [OR=2.2(95%CI:1,96-2.55)]; bathing in rivers/beaches [OR=1.5(95%CI:1.27-1.88)]; mosquito bites [OR=1.5(95%CI:1.38-1.65)]; sexual intercourse <=14 years old [OR=1.4 (95%CI:1.33-1.55)]. Variables inversely associated with low schooling were: being white [OR=0.9 (95%CI:0.82-0.91)]; stating that STD can be transmitted by: sharing syringes/needles [OR=0.7(95%CI: 0.62-0.78)]; mother-to-child transmission [OR=0.6(95%CI:0.58-0.69)]; having used a condom in the last sexual intercourse [OR=0.8(95%CI:0.71-0.85)]; being MSM [OR=0.7(95% CI: 0.60-0.92)]; knowing that sex without condoms increases risk of transmission [OR=0.4 (95%CI:0,37-0,51)]. Given the association of low schooling with less knowledge about STD, educational policies geared to this population are needed because they are more vulnerable.