Tuberculosis is encountering a renewal attention due to emergent causes, linked primarily to migration from high-endemic countries of many subjects who present important risk factors as poverty, homelessness, drug abuse, HIV infection. The purpose of the present study is to evaluate the spread of Mycobacterium tuberculosis in social groups traditionally at higher risk of developing the disease and often difficult to detect. Tuberculin screening with Mantoux intradermal reaction has been carried out on 2014 subjects with one or more risk conditions. We have considered the following risk conditions: extra European community (e-EC), immigrants, nomads, drug dependants, immunodeficients, alcohol dependants, prison inmates living in protected community or home, subjects known to have contact with a TB case with also one or more of the above conditions. A logistic-regression model has been applied to evaluate the association between several social and/or pathological risk factors and Mantoux responsiveness. The population groups examined show higher rates than the Italian population. The majority of risk factors have a significant association (positive or negative) with Mantoux positivity. In particular, if we add to the condition of e-EC (coded as reference category) other conditions (community, contact, prison), the probability of positive Mantoux increases. In fact, the OR values are 2.92 (C.I. 95%=2.23-3.82) for "e-EC migrants + protected communities", 2.35 (C.I. 95%=1.62-3.40) for "e-EC migrants + contact" and 2.53 (C.I. 95%=1.24-5.14) for "e-EC migrants + prison". On the other hand the condition of "e-EC migrants + nomad" appears to be significantly "protective" in relation to Mantoux positivity (OR=0.23; C.I. 95%=0.16-0.33), and the same is true for "protected community + contact", "prison", "drug dependence", "drug dependence + immunodeficiency" with respective OR values of 0.37 (C.I. 95%=0.15-0.93), 0.29 (C.I. 95%=0.14-0.58), 0.20 (C.I. 95%=0.14-0.28) and 0.12 (C.I. 95%=0.04-0.41). There is a sharp difference between those socially organized and those without social reference, who seek occasional and temporary hospitality in available structures.