OBJECTIVE To assess iodine status and goitre prevalence in a sample of schoolchildren in Melbourne. METHODS Cross-sectional study of urinary iodine excretion and presence of goitre in a sample of schoolchildren from Years 5-12 attending two urban schools. METHODS 607 children aged 11-18 years consented to thyroid gland palpation and 577 provided a urine sample on the day of examination in August 2001. METHODS Iodine status of the study population, based on median urinary iodine values categorised as normal (> or = 100 microg/L), mild (50-99 microg/L) or moderate-severe (< 50 microg/L), and classified according to sex, school year and presence of goitre. RESULTS 76% (439/577) of students had abnormal urinary iodine values, with 27% (156/577) having values consistent with moderate-severe deficiency. The median urinary iodine excretion for the total group was 70 microg/L, with values for school years 5-12 ranging from 62 microg/L (Year 12) to 76 microg/L (Year 9). The median urinary iodine value in girls was lower than that in boys (64 microg/L v 82 microg/L), and girls had significantly lower urinary iodine values overall (P < 0.002). There was no association between goitre grade and moderate-severe (< 50 microg/L; P = 0.39) or mild (50-99 microg/L; P = 0.07) urinary iodine deficiency. CONCLUSIONS We found mild iodine deficiency in a cohort of schoolchildren in Melbourne. Our results support other data showing mild iodine deficiency in Sydney and Tasmania and the argument for a national study of iodine nutrition.