OBJECTIVE: An insertion/deletion polymorphism (-94ins/delATTG) in the promoter region of the NFKB1 gene correlates to an increased risk of ulcerative colitis, a known risk factor for colorectal cancer, but this polymorphism has not been studied in colorectal cancer patients. The purpose of this study was to investigate whether this polymorphism is related to colorectal cancer risk and clinicopathological variables. MATERIAL AND METHODS: Case samples were taken from four groups of Swedish patients: 193 unselected patients, 90 patients with > or =3 affected 1st-degree relatives, 85 patients with 2 affected 1st-degree relatives, and 109 sporadic cancer patients, and one group of 193 unselected Chinese patients. Controls included 439 Swedish and 458 Chinese healthy individuals. Genotypes were determined by polymerase chain reaction (PCR)-restriction fragment length polymorphism. RESULTS: The deletion increased the risk of colorectal cancer among Swedish unselected patients (OR =3.81, 95% CI: 2.17-6.69, p 0.05). Similar evidence was seen in age-adjusted analyses (p 0.05). CONCLUSIONS: Deletion of the polymorphism was associated with increased susceptibility to sporadic colorectal cancers in the Swedish population, but not in the Swedish patients with a family history of colorectal cancer or in Chinese patients.