This study explores the association between the systemic immune-inflammation index (SII) and psoriasis using data from the National Health and Nutrition Examination Survey (NHANES) 2009-2014. SII, calculated as (platelet count × neutrophil count)/lymphocyte count, reflects systemic inflammation and immune response. The study found a positive correlation between SII and psoriasis, with higher SII levels associated with an increased risk of psoriasis. This association was significant in women, individuals with a BMI ≥30 kg/m², and non-stroke, non-cancer patients. The relationship between SII and psoriasis showed two consecutive inverted U-shaped patterns, with the most significant inflection point at 797.067. However, after adjusting for all covariates, the significant positive correlation became insignificant. The study highlights the potential of SII as a simple and practical tool for monitoring psoriasis disease activity and treatment efficacy. Despite these findings, the study has limitations, including a cross-sectional design and potential misdiagnosis due to self-reported data. Further large-scale prospective studies are needed to validate these results. The study contributes to understanding the link between systemic inflammation and psoriasis, suggesting that SII could be a useful biomarker for psoriasis and its comorbidities.This study explores the association between the systemic immune-inflammation index (SII) and psoriasis using data from the National Health and Nutrition Examination Survey (NHANES) 2009-2014. SII, calculated as (platelet count × neutrophil count)/lymphocyte count, reflects systemic inflammation and immune response. The study found a positive correlation between SII and psoriasis, with higher SII levels associated with an increased risk of psoriasis. This association was significant in women, individuals with a BMI ≥30 kg/m², and non-stroke, non-cancer patients. The relationship between SII and psoriasis showed two consecutive inverted U-shaped patterns, with the most significant inflection point at 797.067. However, after adjusting for all covariates, the significant positive correlation became insignificant. The study highlights the potential of SII as a simple and practical tool for monitoring psoriasis disease activity and treatment efficacy. Despite these findings, the study has limitations, including a cross-sectional design and potential misdiagnosis due to self-reported data. Further large-scale prospective studies are needed to validate these results. The study contributes to understanding the link between systemic inflammation and psoriasis, suggesting that SII could be a useful biomarker for psoriasis and its comorbidities.