What is goiter and what causes it to grow?

Thyroid enlargement: A goiter is an enlarged thyroid. Most cases are not cancer (but a doc needs to examine you and probably do an ultrasound). The most common cause in the usa is living in an area that has soil that is deficient in iodine. Many goiters seem to run in families. At least 5% of all women have some nodules in their thyroid and this goes up to nearly half if screened with ultrasound.