We present the results of the Mantoux test (5 units tuberculin) survey in the Eastern Province of Saudi Arabia, which was conducted as part of a nationwide epidemiological survey of tuberculosis. A total of 1105 subjects were screened out of whom 630 gave a history of BCG vaccination in the past and 363 were BCG-negative. Among BCG-negative children aged 5-14 years, only 5% had a positive Mantoux, a rate lower than most Third World countries but higher than developed countries were under 2% of children are tuberculin reactors. This calls for continuation of free treatment of active cases and increased efforts towards screening of contacts. The results also vindicate the current policy of giving BCG vaccine at birth and probably indicates the need to revaccinate at school leaving age, in accordance with WHO recommendations. Tuberculin reactivity rose steeply with age (32% at age 15-24 and 72% at age 45-64 years) indicating the presence of a large pool of subjects at risk of breaking into active disease. Finally, 71% (201/283) of children aged 5-14 years who had received BCG vaccine at birth, reacted negatively to the Mantoux test. This supports the findings of previous studies that in the majority of subjects, BCG-induced tuberculin sensitivity fades a few years after vaccination.