Introduction: Iodine is an essential micronutrient and its deficiency can severely impact children’s development. In 2012, the Thyroid Study Group of the Portuguese Society of Endocrinology, Diabetes and Metabolism discovered that the median urinary iodine concentration (mUIC) level in schoolchildren of São Miguel was far too low at 70.9 μg/L. In response, the government implemented a salt iodization program to help normalize levels. This investigation evaluated the efficacy of such an approach. Methods: Urinary iodine concentration (UIC) was evaluated in 362 schoolchildren from São Miguel using the fast colorimetric method. Results: mUIC was 106.7 μg/L, significantly higher than that observed in 2012 ( p < 0.001). Over half (55.5%) of the schoolchildren had a UIC >100 μg/L versus 23.0% in 2012 ( p < 0.001). 9.4% of schoolchildren had a UIC <50 μg/L, significantly lower than the 30.6% reported in 2012 ( p < 0.001). Discussion/Conclusion: Five years after the implementation of the government salt iodization program, the mUIC increased from 70.9 to 106.7 μg/L. This study confirms the efficacy of the adopted measures in schoolchildren population.