To decrease total body iodine is a key point in preparation for radioiodine study and therapy. We introduced a stringent self-managed low iodine diet (LID) and compared the outcome to that of the conventional restricted iodine diet (RID) for outpatients. We measured urine iodine to creatinine ratios (I/Cr) in patients prepared with RID for one week, LID for one week, or LID for two weeks. Mean urinary iodine excretion after RID for one week (n = 210) was 182.2 μg/gCr (range, 13–986 μg/gCr; standard deviation (SD) = 158.5) not reaching below the recommended level (I/Cr<100 μg/gCr). Urinary iodine excretion after LID for one week (n = 15) showed a lower mean urinary iodine level (I/Cr 119.4 μg/gCr; range, 23–218 μg/gCr; SD = 55.9) than RID for one-week, and two-week LID (n = 17) showed an even lower mean level (I/Cr 63.1 μg/gCr; range, 7–134 μg/gCr; SD = 38.7). The one-week LID period adequately (recommended level of I/Cr being less than 100 μg/gCr) prepared 26% of the patients, while two-weeks on the diet adequately prepared 70% of the patients. Furthermore, none of the two-week LID patients had I/Cr>150 μg/gCr, although a significantly greater number of one-week LID patients (19%) did. Our self-managed, outpatient LID successfully induced iodine deficiency, and two-week LID may be recommended for preparation in radioiodine study and therapy for thyroid cancer.