Background As tuberculosis (TB) is highly prevalent among prisoners, it is important that health service professionals and professionals in close contact with prisoners are acquainted with diagnostic, prevention and control basic concepts.

Objectives The aim of this study is to evaluate the differences in knowledge about TB among prison workers and workers of the basic health services (administrative and health professionals).

Method It was designed a cross-sectional study with 115 guards and health professionals of a prison, 121 administrative workers of the health services and 125 health professionals of the health services. Knowledge about diagnosis symptoms, prevention and treatment was sought using a questionnaire based on KAP (knowledge, attitude and practice) survey. Differences among the proportion of affirmative answers were estimated using χ² test with significance level of 0.05.

Results Although the most important symptom for all three groups was cough for more than 2 weeks, administrative and health professionals mentioned it in a higher proportion (84 and 85%) than prison workers (66%) (p<0.05). Weight lost (60%) and fever of unknown cause (32%) did not show statistical difference (p=0.07 and p=0.59). Airborne transmission was correctly informed by 88.4% to 94.4% with no statistical differences (p=0.19) and sharing plates (41%) and shaking hands (5%) were incorrectly mentioned as forms of transmission, also without differences among groups. Supervised treatment (74%–80%) also did not have statistical difference.

Conclusions Although health professionals showed a higher knowledge, 15% gave incorrect answers, thus continued education is needed to improve TB diagnosis and prevention.