To assess the prevalence of low and marginal iodine intake and urinary iodine excretion among adults in the Netherlands and to investigate determinants of urinary iodine excretion.The study population consisted of 444 people aged 20-79 y, balanced for sex and 10 y age classes with an over-representation of people with a low habitual intake of vitamin B6. Food consumption was measured by three day food records and 24 h urine was sampled twice.On average, iodine intake (mean of three days) in men was in the recommended range of 150-300 microg/d, but average intake in women was not. Mean 24 h urinary excretion values confirmed this observation. Estimation of the prevalence of low iodine excretion depended on the parameter chosen (absolute per 24 h, per kg body weight per 24 h, as concentration or per creatinin). The prevalence of low iodine supply, based on intake <100 microg/d (mean of three days) and intake or excretion parameters per creatinin excretion or per kg body weight, varied from 4-14% among adult women and from 5-17% among adult men. The prevalence of marginal iodine intake (<50 microg/d) and excretion was less than 5% in all adult age-sex groups. Urinary iodine excretion was most strongly associated with intake of iodine as such or as bread in combination with urinary excretion of sodium or potassium, confirming the importance of iodized salt (in bread) for iodine status. Age and total energy intake had a relatively minor impact on urinary iodine excretion.