BACKGROUND: The increase of the atopical disorders can be partially explained by two factors, the infectious disease in developed and developing countries, and the changes in immunization programs, infections such as measles, whooping cough or tuberculosis can modify the immune response. Recent studies have demonstrated that an inverse relation could exist between the response to late cutaneus hypersensitivity to Mycobacterium tuberculosis and atopic condition. Also, a strong positive response has been associated with low levels of IgE and Th1 cytokines. However some authors have not found positivity between low prevalence in allergic diseases and PPD. OBJECTIVE: To determine the reaction to PPD in children vaccinated with BCG at birth and its disorders. MATERIAL AND METHOD: The study sample included male and female children from 2 to 7 years old, vaccinated with BCG at birth, this fact was corroborated with the post vaccination scar. They had all been diagnosed with allergic disease with clinical compatible data, positive Prick test, elevated serum IgE, and absence of any associated immune deficiency. RESULTS: A total of 50 patients, with a mean age of 4.7 years (2.0 to 7.7 years) were studied. 72% (36) were males and 28% (14) females. Twenty-two percent had diagnosis of asthma, 8% allergic rhinitis, and 62% both diagnosis. The average diameter of tuberculin induration was of 5 mm; 5 patients (10%) had positive reaction (+10 mm); 23 patients (46%) were between 5-9 mm; 8 patients (16%) between 1-4 mm, and 14 of the patients (28%) without reactivity. CONCLUSION: We demonstrated that the vaccination with BCG do not protect against the development of allergy, and the negative tuberculin response may mean a reduced cell response. So, it is necessary to assess the cell immunity and revaccination with BCG, with determination of immunological markers, before and after, such as IL 4, IL 2, INF and allergy symptoms.