The authors describe the principal clinical and pathological aspects of the solitary hyperfunctioning adenoma or the multifocal hyperfunction of a multinodular goitre. Successively they report the incidence of these conditions in countries with different iodine intake as well as the age distribution of the examined patients. In the area with low iodine intake the incidence of hyperthyroidism caused by multinodular goitre is 10 times higher than in the high iodine intake area. Finally, the role of the laboratory in the diagnosis of hyperthyroidism and in identifying the type of hyperthyroidism is discussed; an up-todate flow-sheme is also reported.