To determine the prevalence and incidence of LTBI among prison guards and to the risk factors associated with infection. Two male prisons in Medellín and Itaguí, Colombia. A cohort study was conducted in adult prison guards that consented to participate. Exclusion criteria included: previous or current active TB, or conditions that preclude TST administration. We screened 194 guards and completed 155 TST administrations. The prevalence of LTBI was 55.8% in prison one, and 39.1% in prison two. The risk factors associated with LTBI diagnosis included drug use at least once in a lifetime (PR: 1.75; 95% CI 1.42-2.15) and male sex (PR: 2.16; 95% CI 1.01-4.62). The cumulative incidence of TST conversion over 6 months was 3.2%. All conversions occurred in prison 1. Our findings suggest an occupational risk for LTBI prevalence and incidence among guards (different prevalence and incidence according to the prison they work).