Goitre has been declining in Italy since the 1970s and because active prophylaxis (AP) has been very limited, it has been suggested that in most places the decline was due to silent prophylaxis (SP). SP is related to the natural increase in iodine intake because of higher consumption of iodine-rich products associated with socioeconomic development. The hypothesis tested in the present study is that SP has increased iodine intake in Italy with subsequent reduction of goitre and that such changes can be quantified. The analysis is based on surveys carried out between the 1970s and the 1990s where goitre and urinary iodine, a proxy of consumption, were measured in schoolchildren. The contribution of the SP can be quantified in an annual increase in urinary iodine excretion between 2.1 and 4 microg/l, and an annual decline in goitre prevalence between 2.1 and 3.6 %. In the few areas with AP, there was an annual increase in urinary iodine between 6.5 and 13.1 microg/l, while the average annual decline of goitre was between 4.4 and 10 %. The present results could be used by policy-makers to predict the future trends in the excretion of urinary iodine and prevalence of goitre in Italy with and without AP. AP is about three times faster than SP in increasing iodine intake, but policy-makers should estimate the incremental cost-effectiveness of AP net of the iodine increase already occurring naturally with the SP.