The measurement of iodine is a widely accepted method to explore iodine disorders. The most precise estimation is the determination of the urinary iodine in 24-hour collections. Urine collection is notoriously difficult to obtain, specially in children. In these conditions, serum measurement could be a method to overcome these limitations. We describe a colorimetric method adapted on a microtiter plate, with optimized serum mineralization conditions. The method is linear to 2400 nmol/L with a detection limit of 75 nmol/L. Precision is below 10%. The method was validated against one automatic technique. We conclude that this relatively simple method could be an additional tool to explore dysthyroidism.