Long term follow-up study of thyroid cancer at Presbyterian Hospital, N. Y. C, has shown that certain characteristics of the disease may be used as criteria in deciding whether a nodular goiter is probable cancer or not. The recognition of nodularity itself is very important, but not necessarily the consistency of the nodules. Diffusely enlarged glands, toxic goiters of any type, goiters with multiple nodules in older individuals are not likely to be cancerous. Nodular goiters in children, juveniles and young adults should be considered cancer until proved otherwise, especially if, in association with the nodular goiter, nodules are present in the neck outside the thyroid area. Nodules thought to be solitary and discrete at any age must be suspected strongly of being cancer unless definitely toxic. The surgery of nodular goiter based on these facts and other characteristics of thyroid cancer are discussed.