In many parts of the world endemic goitre and cretinism are as prevalent today as they were in the past although easily applied methods of prevention are available at a nominal cost. In some countries there are difficulties of transport and communications, and administrations may be preoccupied with other health and social programmes. The effects of endemic goitre are generally not at all obvious and a programme of prevention therefore offers few political attractions. Also, the medical profession has in some instances been concerned about the possible adverse effects of prophylaxis with iodine. The result is that many millions of people all over the world suffer from goitre and its attendant disabilities, and areas exist where endemic cretinism is common. This article is offered as a guide to government agencies and public health personnel on the detection of endemic goitre, the assessment of its severity, and the initiation and monitoring of preventive programmes under various field conditions.