A cross-sectional survey of 785 schoolchildren living in the Al An region was undertaken between January and June 1994 to assess the effect of neonatal BCG vaccination on tuberculin sensitivity and to study the risk of exposure to tuberculosis in the same population. A documented history of BCG vaccination was obtained in 547 (69.7%) schoolchildren. The prevalence of a 10 mm or greater induration of tuberculin skin reactivity varied from 8% in unvaccinated to 11.5% among vaccinated children. This was not statistically significant. Children living in urban areas irrespective of vaccination status had a higher rate of tuberculin reactivity than those living in rural areas (relative risk 5.77; 95% confidence interval 1.85-18.00; p<0.0004). The pattern and rate of tuberculin sensitivity were similar among the other socio-demographic standards investigated. Earlier BCG vaccination had no effect on subsequent tuberculin sensitivity of either negative (0.4 mm), intermediate (5-9 mm) or positive (greater than or equal to 10 mm) type skin reactions. It is concluded that the risk of exposure to tuberculous infection is several times higher among children living in urban areas than among those living in a rural environment. Earlier BCG vaccination should not interfere with diagnostic tuberculin skin sensitivity and is still a useful tool in assessing the risk of tuberculous infection in such populations.