Objective：To investigate the association between congenital simple absence of axillary hair and Hashimoto’s thyroiditis （HT）. Methods：A total of 116 patients with thyroid diseases were divided into two groups according to the presence or absence of congenital simple absence of axillary hair：52 patients with congenital simple absence of axillary hair as group A and 64 patients without congenital simple absence of axillary hair as group B. In group A，there were 5 male patients and 47 female patients；the mean age was 35.3±11.5 years；there were 46 HT patients，2 Graves’ disease（GD） patients，and 4 thyroid carcinoma（TC） patients. In group B，there were 26 male patients and 38 female patients；the mean age was 41.4±12.6 years；there were 25 GD patients，2 HT patients，19 TC patients，13 nodular goiter patients，and 5 subacute thyroiditis patients. All patients underwent physical examination for sex hair and the thyroid，thyroid function test，measurement of thyroid autoimmune antibodies，and thyroid ultrasound. Results：The proportion of HT patients in group A was significantly higher than that in group B（98.06% vs. 3.13%，P=0.000）. Among all patients in group A，55.77% had a family history of congenital simple absence of axillary hair，44.23% had a family history of thyroid diseases，26.54% had hypothyroidism，and 94.21% were positive for thyroid peroxidase antibody thyroglobulin antibody，and these proportions were significantly higher than those in group B（P=0.000，0.029，0.000，0.000，and 0.000）. Conclusion：Congenital simple absence of axillary hair may be a genetic marker of HT，thus providing clinical evidence for early identification of HT patients and timely inter－vention.