The relationship between malnutrition, goitre and thyroid hormones was studied among Aborigines and Malays in Ulu Langat, Malaysia. Fifty Aborigines aged >=7years were selected randomly for anthropometric, clinical and hormonal assessment. Fifty Malays of similar age from the nearby Malay village were chosen as controls. The Aborigines had a higher prevalence of malnutrition and goitre compared to the Malays. The prevalence of goitre was 26.5% amongst Aborigines and 19.6% among the Malays. All the nutritional indexes measured were significantly different between the two communities, especially among females. The differences corresponded to significant differences in levels of thyroid-stimulating hormone (TSH) measured using a highly sensitive TSH assay. By univariate analysis the increase in TSH corresponded to the decrease in body mass index (BMI). On the other hand, no association was found between BMI and goitres. No thyroid autoantibodies were detected and all subjects were clinically euthyroid and had normal thyroxine and triidothyronine levels. However, consumption of cassava conferred a four-fold risk of developing goitres. The high prevalence of goitres in malnourished subjects in this region which is not known to be iodine deficient could be due to cassava consumption.