Thyroid neoplasm.

Solitary nodules, in general, are more likely to be neoplastic than are multiple nodules.

Nodules in younger patients are more likely to be neoplastic than are those in older patients.

Nodules in males are more likely to be neoplastic than are those in females.

A history of radiation treatment to the head and neck region is associated with an increased incidence of thyroid malignancy.

Nodules that take up radioactive iodine in imaging studies (hot nodules) are more likely to be benign than malignant.