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This study aims to investigate the relation between inflammatory markers such as neutrophil-to-lymphocyte ratio (NLR), lymphocyte-to-monocyte ratio (LMR), platelet-to-monocyte ratio, and suicide attempts in adolescents with bipolar disorder and to define a patient phenotype based on inflammatory markers. All patients under 18 years old diagnosed with bipolar disorder type I according to the diagnostic and statistical manual of mental disorders-5 criteria were included the study. NLR, platelet-to-lymphocyte ratio, LMR, and neutrophil-to-monocyte ratio were calculated. The median-split classification yielded 12 distinct inflammatory phenotypes (low-high-high-high [LHHH], low-low-low-low, high-high-high-high, low-low-high-high, low-high-high-low, high-low-low-high, high-high-low-low, low-high-low-low, high-high-low-high, low-low-high-low, high-low-high-high, and high-low-low-low). A total of 145 patients with bipolar disorder type I were included in the analysis. Thirty-five patients (24.1%) had a lifetime history of suicide attempts. None of the 4 inflammatory ratios differed significantly between patients with and without suicide attempt history (NLR: 1.93 ± 0.93 vs 2.11 ± 1.49, P = .864; platelet-to-lymphocyte ratio: 122.37 ± 41.74 vs 123.64 ± 50.23, P = .837; LMR: 3.97 ± 1.66 vs 3.76 ± 1.33, P = .600; neutrophil-to-monocyte ratio: 6.91 ± 2.49 vs 7.14 ± 4.59, P = .762). We identified 12 distinct inflammatory phenotypes represented markedly different suicide risks ranging from 0% to 57.1% (LHHH: 57.1%, low-low-low-low: 40%, high-high-high-high: 35.7%, low-low-high-high: 30.8). The LHHH phenotype, characterized by low NLR but high other ratios, emerged as a particularly high-risk profile requiring intensive clinical attention. The inflammatory phenotypes identified here may be a first step toward biologically informed suicide prevention in bipolar disorder.