This study was performed to measure the annual infection rate in Sohag city taking the preparatory school children as a mirror to the size of the population. Subjects : 1000 pupils were included in the study 500 males and 500 females. The pupils were in the 1st year of the preparatory schools in Sohag city. Mantoux tuberculin test was done to the pupils by injecting P.P.D 5 T.U intradermally in the volar surface of the forearm waiting for 72 hours, then the diameter of the induration but not the erythema was measured by transparent ruler in the transverse and longitudinal directions, the mean of the diameter was obtained. The diameter of 10mm or more was considered as positive. After one year the negative tuberculin tested pupils are tuberculin retested in the same steps as before. All pupils were subjected to through and careful history taking especially regarding factors which are age, sex, residence, socio-economic state, B.C.G vaccination, contagious state to active pulmonary tuberculous patient and the presence of medical disease in the converters. All pupils were subjected to careful general and chest examination and inspection to the deltoid regions for B.C.G scar. All positive tuberculin test in the tested and retested pupils are subjected to mass miniature radiography M.M.R) and sputum exam. For acid fast bacilli (AFB). From the tabulated data it was found that the prevalence of T.B infection in all pupils 25%. The prevalence of T.B infection in non vaccinated pupils 23.3%. The annual infection rate in Sohag city is 0.8 % which show marked decrease if compared to that made in Egypt in 1952 which was 3.4%. Tuberculin positive children either in the tested or the retested pupils is higher in older children. The conversion rate is higher in boys. The conversion is higher in rural inhabitant children. The conversion is higher in B.C.G-negative children. Induration of 5 mm or more of the tuberculin test is a good indicator than 10mm or more as a reflection of B.C.G. vaccination. There is weak relationship between medical disease and the converters in this study. The infection rate and the conversion rate is higher in low socioeconomic conditions.