Background: Iodine deficiency occurs in West European countries. Iodine is important for brain development of the foetus and infant. The current iodine status of pregnant and lactating Dutch women is unknown. Methods: In a pilot study we examined the iodine status of 36 women. From 20 gestational weeks (GW) until 4 weeks postpartum, they ingested 150 mu g iodine/day in the form of a multivitamin supplement for pregnant and lactating women. Twenty-four hour urine samples were collected at 20 and 36 GW and at 4 weeks postpartum. A breast milk sample was collected at 4 weeks postpartum. Iodine concentrations were analysed by inductively coupled plasma-mass spectrometry. Cut-off values for the urinary iodine concentration (UIC) for pregnant and lactating women are 150 and 100 mu g/l, respectively. Adequate intakes (AI) of iodine for infants aged 0-6 months are 1.1 mu mol/l (Institute of Medicine recommendations) or 0.5 mu mol/l (Nordic Council recommendations). Results: The median UICs (percentages below cut-off) were 102 mu g/l (83%) at 20 GW, 144 mu g/l (56%) at 36 GW and 112 mu g/l (40%) at 4 weeks postpartum. The median breast milk iodine concentration was 1.2 mu mol/l (range 0.5-3.0); 33% and 0% of the infants had estimated iodine intakes below the IOM-AI and Nordic-AI, respectively. Conclusion: This pilot study suggested a high prevalence of iodine deficiency during pregnancy. Daily supplementation of 150 mu g iodine from 20 GW might be insufficient to reach maternal iodine adequacy. The median breast milk iodine concentration seems adequate. Further studies, using a representative sample of the Dutch population, are needed to establish the current Dutch iodine status of pregnant and lactating women.