Adequate iodine supply is necessary for normal thyroid function and size. The main source of iodine in most developed countries is iodized salt. In Slovenia, salt is iodized with 25 mg of potassium iodide per kg, which ensures an adequate iodine supply to the general population. Iodine deficiency may occur in individuals consuming less salted or even unsalted food. In a 27-year-old man who had consumed uncooked and unsalted vegetarian food for 4 years, we diagnosed severe hypothyroidism and a large goiter with a volume of 107.4 ml, which was approximately four times its normal size. With investigations, autoimmune thyroid disease and other frequent causes of hypothyroidism were excluded. Goiter and hypothyroidism were attributed to the severe lack of ingested iodine and to the inhibitory effect of thiocyanates from raw vegetables on iodide transport into the thyrocyte. For six months, the patient was treated with a combination of L-thyroxine and iodide, followed by iodide tablets only. He also stopped eating fresh unsalted food. After a year and a half, his thyroid gland was four times smaller and its function had returned to normal. Long-term consumption of completely unsalted food may cause severe iodine deficiency, which leads to significantly increased thyroid growth and severe hypothyroidism.