Objective. To identify causes of persistence of endemic goiter in specific areas in Mexico, despite a mandatory salt iodination program established since the early 1960s. Results. In the mountainous state of Hidalgo school-age children (SAC) had a prevalence of goitre between 6% (capital city) - 21.2% (tropical low-lands). Prevalence of low (50 ppm). Goitrogens included consumption of yucca, sweet potato, broccoli and cauliflower; 24% of the population consumed water from wells contaminated with E. coli or heavy metals (arsenic and mercury). In the coastal state of Colima, goiter in SAC had a prevalence of 21 4%, with low UIE in 19.5% and high UIE in 32.0%. 92% of the population used coarse-grain ocean salt, with 86.8% of locally-iodized salt samples