Goiter remains to be a significant problem and the prevalence has been increasing in Turkey. There are at least four large endemic goiter regions and the prevalence ranges between 36-69% in these areas. Previous studies showed low iodine levels in the soil and in drinking water in the endemic areas. Daily dietary iodine intake was also found to be low in the endemic areas. In the present study the mean urinary iodine level of the non-endemic control area was at 92.66 +/- 28.80-mu-g/day. This level is lower than the WHO's optimal level (150-300-mu-g/day). The mean iodine level of the control group in the endemic area was 80.2 +/- 19.07-mu-g/day. In the endemic area urinary iodine levels decreased as the size of the gland increased, being 77 +/- 27.30-mu-g/day in Grade I patients, 71.2 +/- 19.81-mu-g/day in Grade II patients, 70.7 +/- 21.05-mu-g/day in Grade III patients, 68.1 +/- 14.93-mu-g/day in Grade IV. patients. As a result, the urinary iodine levels in non-endemic and endemic areas of Turkey are low and the values are lower in the endemic areas. The mass prophylaxis by iodine has not yet started in the endemic regions. The iodinization of dietary salt which is cheap and practical would seem to be the best way in the mandatory propylaxis in Turkey.