Background: Crohn's disease (CD) is a chronic inflammatory bowel disease often accompanied by periodontal symptoms. Based on its function in immune response tumour necrosis factor-alpha (TNF-a) and its genetic variants have been discussed as risk indicators in inflammatory processes. Therefore, the aim of the present study was to investigate the impact of TNF-a polymorphisms on periodontal parameters and inflammatory lesions of oral mucosa as a characteristic of CD. Patients and methods: A total of 142 patients with CD were included in the study. Oral soft tissue alterations and periodontal parameters were assessed. Genotypes, alleles, and haplotypes of TNF-a polymorphisms (rs1800629: c.-308G>A and rs361525: c.-238G>A) were determined by polymerase chain reaction with sequence-specific primers (PCR-SSP). Results: CD patients who exhibited more severe oral soft tissue alterations were significantly more often A allele carriers of rs361525 than G allele carriers (14.2% vs. 2.2%; p0.001). Furthermore, A allele carriers had a higher mean periodontal probing depth (p0.05), mean clinical attachment level (p0.05) and sites with bleeding on probing (n.s.). Similar results were obtained evaluating A allele containing genotypes (AG+AA) and haplotype (GA). In multivariate analyses considering age, gender, smoking, and medication as cofounders, the A allele was proven to be an independent risk indicator for oral soft tissue alterations in CD patients. No genotype dependent influence of rs1800629 was observed. Conclusions: TNF-a A allele of rs361525 represents a significant risk indicator for oral soft tissue alterations in CD patients. Keywords: TNF-a, genetic, Morbus Crohn, periodontitis