The purpose of this paper was the determination, in the endemic goiter area of Teano (Caserta, Italy), of: i) The goiter prevalence in a group of 920 patients who attended the Outpatient Endocrinology Department; ii) The urinary iodine excretion in 150 adults (20-73-year-old) and 502 children (10-16-year-old; iii) The thyroid size in the 502 children; iv) The environmental iodine levels. Out of 920 patients a total of 750 (81.5%) goiters were detected. Out of these 750 cases, 415 (55.3%) were of grades 1b and 2, 335 (44.7%) of grades 3 and 4. A statistically significant association between goiter size and age was found (p less than 0.05). Laboratory data were entirely available for 506 goitrous patients. Serum TG levels was increased with goiter size and age, whereas there was a progressive decrease in mean serum TSH levels with increasing goiter size and age. The screening program performed on 502 schoolchildren aged 10 to 16 yr found a 68.3% prevalence of grade 1 goiter and a mean urinary ratio iodine/creatinine of 52 +/- 32 (SD) micrograms/g. A mean urinary ratio iodine/creatinine of 60 +/- 27 (SD) micrograms/g was reported in a sample of 150 adult inhabitants. Iodine measurements in water supplies showed levels equal to or less than 1 microgram/l. The area investigated can be identified as a moderate iodine deficient area and classified as grade 1-2 according to the Pan American Health Organization criteria.