BACKGROUND: Tuberculosis (TB) is a major issue in prisons of low and middle income countries where TB incidence rates are much higher in prison populations as compared with the general population. In the Rio de Janeiro (RJ) state prison system, the TB control program is limited to passive case-finding and supervised short duration treatment. The aim of this study was to measure the impact of X-ray screening at entry associated with systematic screening on the prevalence and incidence of active TB. METHODS: We followed up for 2 years a RJ State prison for adult males (1429 inmates at the beginning of the study) and performed, in addition to passive case-finding, 1) two "cross-sectional" X-ray systematic screenings: the first at the beginning of the study period and the second 13 months later; 2) X-ray screening of inmates entering the prison during the 2 year study period. Bacteriological examinations were performed in inmates presenting any pulmonary, pleural or mediastinal X-ray abnormality or spontaneously attending the prison clinic for symptoms suggestive of TB. RESULTS: Overall, 4326 X-rays were performed and 246 TB cases were identified. Prevalence among entering inmates remained similar during 1st and the 2nd year of the study: 2.8% (21/754) and 2.9% (28/954) respectively, whereas prevalence decreased from 6.0% (83/1374) to 2.8% (35/1244) between 1st and 2nd systematic screenings (p < 0.0001). Incidence rates of cases identified by passive case-finding decreased from 42 to 19 per 1000 person-years between the 1st and the 2nd year (p < 0.0001). Cases identified by screenings were less likely to be bacteriologically confirmed as compared with cases identified by passive-case finding. CONCLUSIONS: The strategy investigated, which seems highly effective, should be considered in highly endemic confined settings such as prisons.