To determine the frequency of Tuberculin positives in the diabetic population attending our Health Centre, with readings at three and seven days. Of less importance, to assess how often patients present conversion after a second Tuberculin test, seven days after the first; and to determine the frequency of Tuberculin positives in diabetics in relation to whether they are over or under 65. A transversal observational study. Pío XII Health Centre, Ciudad Real. Patients registered as diabetic in the eight General Medicine clinics and who attended for the customary check-ups. PPD was administered to 163 diabetics and the test was read at three and seven days; if this last reading was negative, a second test was carried out and evaluated at three days. At three days 42.2% were positive; at seven, there was an increase of 6.5% of the total. A second test was performed on 78 patients, which provided an increase in patients with tuberculous infection of 7.14% of the total. There was a statistically significant relationship (p < 0.001) between the positive responses of the first Mantoux and age. There is a high prevalence of Tuberculin positive patients, which increases when another reading is done seven days after the Mantoux; as it does after a second test, by which a retreat in these patients' response to Tuberculin was observed.