© 2014, Springer Science+Business Media New York. Background: Iodine deficiency and obesity are worldwide-occurring health problems. Our purpose was to investigate the relationship between morbid obesity and iodine status, including subjects who lost weight after bariatric surgery. Methods: Ninety morbidly obese women, 90 women with at least 18 months follow-up after bariatric surgery, and 45 healthy non-obese women were recruited. Urinary iodine concentration (UIC) was measured in a spot urinary sample and expressed as the iodine-to-creatinine ratio. Results: Obese women showed a significantly lower UIC in comparison with non-obese women (96.6 (25.8–267.3) vs. 173.3 (47.0–493.6) μg/g; p < 0.001), with a lesser proportion of subjects with adequate iodine status (46.6 vs. 83.3 %, p < 0.001). The mean UIC significantly increased among women who underwent bariatric surgery before the collection of the urinary sample (96.6 (25.8–267.3) vs. 131.9 (62.9–496.4) μg/g; p < 0.001). No difference in UIC was detected between laparoscopic Roux-en-Y gastric bypass and laparoscopic sleeve gastrectomy. Univariate analysis showed that UIC negatively correlated with body mass index (BMI) (r = −0.278, p < 0.001) and positively with age (r = 0.206, p = 0.002). Finally, multiple linear regression analyses showed that BMI was independently associated with UIC (beta = −0.312, p < 0.001; R<sup>2</sup> = 0.166). Conclusion: Obesity is an independent risk factor to iodine deficiency, almost in women. Whether more obese population needs to be considered as a vulnerable group and whether bariatric surgery can reverse iodine deficiency still remain to be elucidated.