The association of Hashimoto Thyroiditis (HT), primary hypothyroidism (PH) and Turner Syndrome (TS) is frequently mentioned in the literature, but studies on its prevalence are rare. In order to verify the frequency of this association, data from a group of 75 patients with TS evaluated at our service from January 1981 to February 1995 were retrospectively analysed. The diagnosis of TS was stablished by karyotype analysis, that of HT by the presence of positive anti-thyroid antibodies and the diagnosis of PH by the detection of elevated ultra-sensitive TSH levels. The mean age of TS diagnosis was 12 years old (from birth to 32 years old); 33 (24%) had a 45,X karyotype and 51 exhibited mosaicism or structural aberrations of sex chromosomes. In 12 of the 75 patients no hormonal investigation was done. Among the 63 remaining patients, 17,4% (11) had HT and/or HP: 12,7% (8) exhibited HT and HP, 3,2% (2) only HT and 1,6% (1) only HP. The mean age of diagnosis of HT and/or HP was 18 years old, 4 cases were diagnosed before 14 years old. Although the frequency of HP in this sample is similar to that found in the international literature and the frequency of HT seems to be lower, the evaluation of thyroid function must be done as a routine in all girls with TS.