The aim of this study is to estudy lingual and labial microcirculation differences among healthy subjects and those with Hashimoto's thyroiditis affected by macroglossia. Twenty healthy patients and 20 patients suffering from Hashimoto's thyroiditis were examined. Labial and lingual capiUaroscopy were used to investigate the characteristics of microcirculation. For each patient we evaluated visibility, course, tortuosity and the possible presence of microhaemorrhages, average calibre of capillary loops and the number of visible capillary loops per square millimetre. The investigations of the labial and lingual mucous were simple, non invasive and repeatable for each patient. In Hashimoto's thyroiditis patients it was possible to observe a wide vascular architectural disorganisation, morphologic anomalies of the capillary loops, loosening of the U shape, reduced capillary diameter This study shows that capillary alterations in patients suffering from Hashimoto's thyroiditis occur in the labial and lingual mucous microcirculation. In the patients affected by macroglossia a reduced number of capillary density was observed and it was correlated to the deposition of proteinaceous ground substance