Desferrioxamine (DFO), an iron-chelating drug, up to today has been essential for the care of thalassaemic patients. Unfortunately it presents some toxic effects. One of these is sensorineural hypoacusia, already reported some years ago. In 1987 we documented in our patients a prevalence of 19.4% (7 cases of 36) of sensorineural hypoacusia that proved to be significantly associated with the highest pro kg/die doses of DFO. We made a follow-up audiometry over a 5-year period after a general adjustment of the DFO dosage related to serum Ferritin levels. Four patients with mild hypoacusia (30-50 dB) showed normal audiometry after one year. The hypoacusia of the two severe cases (50-80 dB) proved stable until 5-years later in one case and increased in the other. Only a new case arose denovo. In pathologic patients "Therapeutic index" (DFO/serum Ferritin) was significantly higher than in normoacusic ones and the "threshold" value between the two populations was of 0.027. We think that the Therapeutic index may be a useful guideline to calculate safe doses of DFO about ototoxicity.