We carried out a case-control study is to investigate the relationship between iodine deficiency and stomach cancer. We compared the ratio of urinary iodine to urinary creatinine in 100 patients diagnosed with stomach cancer and 84 people in a control group. Mean urinary iodine levels were lower in the patients with stomach cancer, 61.9 microg/g creatinine, compared to 101.7 microg/g creatinine in the control group (P < 0.0001). More of the cancer patients (49.0%) had severe iodine deficiency (< 25 microg/g creatinine) than people in the control group (19.1%) (P< 0.0001). We found the relationship between stomach cancer and iodine deficiency to be significant.