In this review we summarize the most recent advances of flow and image cytometry, cytogenetics and molecular genetics of tumours and tumour-like lesions of the thyroid, especially focusing on the putative relationship between nodular goitres and adenomas, the differential diagnosis of benign and malignant neoplasms and the pathogenesis and prognosis of carcinomas. Data obtained by in situ hybridization and immunohistochemical detection of proliferative markers, metal binding proteins and oncogenes, anti-oncogenes, growth factors and growth factor receptors are also used whenever appropriate.