To determine iodine levels in salt and iodine deficiency prevalence in school-aged children in 16 districts in Tanzania with previous severe iodine deficiency.

A cross-sectional study in schoolchildren. Systematic probability sampling was used to select schools and subjects for goitre assessment and urinary iodine determination.

Sixteen districts randomly selected from the 27 categorised as severely iodine-deficient in Tanzania.

The study population was primary-school children aged 6–18 years who were examined for goitre prevalence and urinary iodine concentration (UIC). Salt samples from schoolchildren's homes and from shops were tested for iodine content.

The study revealed that 83.3% of households (n = 21 160) in the surveyed districts used iodised salt. Also, 94% of sampled shops (n = 397) sold iodised salt, with a median iodine level of 37.0 ppm (range 4.2–240 ppm). Median UIC in 2089 schoolchildren was 235.0 μg l− 1 and 9.3% had UIC values below 50 μg l− 1. The overall unweighted mean visible and total goitre prevalence was 6.7% and 24.3%, respectively (n = 16 222). The age group 6–12 years had the lowest goitre prevalence (3.6% visible and 18.0% total goitre, n = 7147). The total goitre prevalence had decreased significantly in all districts from an unweighted mean of 65.4% in the 1980s to 24.3% in 1999 (P < 0.05). We believe this difference was also biologically significant.

These findings indicate that iodine deficiency is largely eliminated in the 16 districts categorised as severely iodine-deficient in Tanzania, and that the iodine content of salt purchased from shops is highly variable.