Prevalence, clinical manifestations and therapeutic requirements of thyroid disorders greatly differ during life-time. There are a variety of diagnostic and therapeutic problems in pregnant women which are relevant not only to the endocrinologist, but also to the pediatrician and the gynecologist. The development of fetal thyroid and the pathogenesis of genetic diseases are only partly understood. Screening of thyroid diseases in the newborn and early treatment are often inconsequentially performed. In puberty, early diagnosis and prevention of thyroid diseases are of tremendous socio-economical relevance as most goiters develop at this age. In adults, iodine deficiency remains a world wide risk responsible for morbidity resulting from nodular goiter and thyroid autonomy. Iodine excess is a common cause of iatrogenic thyroid disorders. Thyroid diseases in the elderly are often unrecognized and may substantially contribute to morbidity and mortality. It is the aim of this book to focus the attention to age dependent aspects of thyroid diseases and their specific diagnosis and treatment.