Professor Hay was born in Kilmarnock and had his university education in Glasgow and Edinburgh. He trained in internal medicine and endocrinology in Scotland and the USA. In 1983 he was invited to join the staff of the Mayo Clinic where he combined for more than forty years a demanding clinical practice with a research career investigating the commonest endocrine malignancy, papillary thyroid carcinoma (PTC), in both adults and children. His published work influenced both American and European Thyroid Cancer Clinical Guidelines and he received many international awards for his scholarly research, which he continues to pursue. His work led globally to a selective use of radioiodine ablation of the thyroid remnant in postoperative PTC management and he introduced in 1991 a novel therapy (ethanol ablation) to eliminate cervical recurrences of PTC. Outside of the clinic, his other interests include golf, motorsport, comedy, music, the theatre, art, architecture and the cartography of Scotland and America.