SummaryBackground: Interleukin-6 (IL-6) is an inflammatory mediator linked to nasal polyposis and asthma, with a single nucleotide polymorphism -174 G/C that seems to promote an inflammatory status. We aimed to analyze the relationship between this polymorphism and asthmatic nasal polyposis patients. Methodology:Cross-sectional study to investigate IL-6 -174 G/C genotypes of 45 nasal polyposis with asthma patients, 63 nasal polyposis-only patients, 45 asthma-only patients and 81 subjects without both diseases. Aspirin intolerance and atopy were main exclusion criteria. IL-6 genotyping was performed using the PCR method with specific primers followed by restriction enzyme analysis, classifying patients in GG, GC or CC genotype. Results:The GG genotype was the most frequent in all inflammatory groups. Less than 40% of controls presented with the GG genotype. There were significant differences between inflammatory groups and control group. No significant differences were seen when comparing inflammatory groups to each other, other than between nasal polyposis-only group and asthma-only group. Conclusion:The IL-6 74 GG genotype was found more frequently in all inflammatory groups than in controls. This genotype could influence nasal polyposis and asthma, and seems to be more important in the latter.