A study was conducted to compare the urinary iodine concentrations in populations from Pahang, Central Malaysia, with those in the capital city Kuala Lumpur, and to compare those of Malays from villages at Batu Talam, Batu Malim, FELDA Sungai Koyan and Hulu Sungai with neighboring aboriginal settlements at Lanai and Buntu. Two hundred and forty urine samples were collected randomly among the population (male 1 1 1 and female 129). The urinary iodine concentrations, measured by the ashing method, among Malays were as follows: Batu Talam 1.1-7.6 micrograms/dl, Batu Malim 1.4-6.6 micrograms/dl, FELDA Sungai Koyan 0.5-6.9 micrograms/dl and Hulu Sungai 0.6-9.9 micrograms/dl. Among aborigines, the urinary iodine levels were 0.1-2.9 micrograms/dl in Lanai and 1.7-6.5 micrograms/dl in Buntu. There was a significant difference in the levels of urinary iodine with regard to gender, but not regarding age. The aborigines had significantly lower iodine levels than Malays (P < 0.001). This difference was also significant with regard to location. The urinary iodine content in Kuala Lumpur was the highest and that in the aboriginal Lanai village was the lowest. Thus, the study showed that the levels of iodine in the urine were influenced by ethnicity and geographic location.