Among the epidemiological barometers useful in evaluating tuberculosis, the Annual Infection Risk is the one which has been shown to be the most useful. This rate can be calculated indirectly (by way of Tables) or directly (by testing the same group of individuals twice over a one-year period). The most ideal method for making these calculations, by consecutively having the same population of 6 year-olds at intervals over a one-year period, is presented. The results indicate a statistically significant difference (P less than 0.001) between the two methods, an indirect AIR of 0.079 to 0.118 being obtained, as related to a Case Rate of 0.44. The fact that said difference is probably due to the impact of the BCG vaccination, which leads to pressure phenomena, and finally, whilst we are not free of said vaccination, this index should be calculated indirectly, based on tuberculosis infection prevalence rates.