Goitre is common among growing children and adolescents. To define the aetiology of goitre in adolescents of Hong Kong and to examine their current level of iodine intake, this cross-sectional survey of goitre in high school students was performed and urine samples were collected for the analysis of iodine excretion. Screening examinations were carried out in 2439 secondary school students aged 12-18 years from ten randomly selected high schools in Hong Kong. Blood samples were obtained from all goitrous subjects for the determination of serum TSH, free T4 and thyroid antibodies. We obtained 476 random urine samples and 80 24-h urinary collections for the analysis of iodine excretion. Of these, 85 subjects (3.5%) had goitre, 70 had simple goitre. Chronic lymphocytic thyroiditis was found in ten subjects. Two had Graves' disease and three had nodular goitre. The median urinary iodine concentration for the random urine samples was 190 microg/l (1.50 micromol/l) or 158 microg/g creatinine. The median 24-h urinary excretion of iodine was 189 microg (1.49 micromol) per day.This cross-sectional study demonstrates the spectrum of thyroid disease in Chinese adolescents in Hong Kong. Their urinary iodine excretion was adequate and much higher than those of children from many European countries and coastal cities of China.