Cyanide exposure from consumption of insufficiently processed cassava has been implicated in aggravating iodine deficiency disorders (IDD). The cyanide metabolite, thiocyanate (SCN) may interfere with iodine (I) uptake of the thyroid gland. A study on 217 women in an IDD endemic area in western Tanzania showed that 98% consumed cassava daily. Total and visible goitre rates were 72.8% and 13.3%, respectively. Median urinary iodine was 3.6 micrograms/dl indicating moderate iodine deficiency. Processing methods which remove cyanogens from cassava roots have changed with time. Urinary thiocyanate (mean; 128 mumol/l) was moderately increased, but women who frequently milled cassava had significantly lower urinary thiocyanate levels. This indicates that mechanical milling could reduce the goitrogenic potential of cassava and we conclude that IDD in the studied area is mainly due to iodine deficiency and sustainable iodine supplementation should be given highest priority.