Background <p>Leptomeningeal metastasis (LM) arising from solid tumors signifies a late-stage complication in the cancer trajectory, often portending a poor prognosis. The prognostic factors remain elusive. Prior research has established the Neutrophil-to-Lymphocyte Ratio (NLR) as an independent prognostic marker in various malignancies; however, its prognostic utility in LM patients remains underexplored. This study aims to investigate the prognostic significance of NLR at the time of LM diagnosis.</p> Patients and methods <p>We conducted a retrospective analysis involving 490 diagnosed LM patients with solid tumor origins at Zhejiang Cancer Hospital. NLR was computed at the time of LM diagnosis. Kaplan-Meier curves and Cox proportional models were employed to examine the association between NLR and overall survival (OS).</p> Results <p>Following exclusions, the cohort comprised 384 patients. The median age was 55 years (interquartile range, IQR: 51-61.25), with a median OS was 6.45 months (IQR: 2.1–15.6) and a median NLR was 4.09 (IQR: 2.81–7.57). The median interval between LM diagnosis and NLR assessment was 1&#xa0;day (IQR: 0–3). NLR proved effective in stratifying the prognosis of LM patients (HR = 1.02, 95% CI 1.01–1.04, <i>p</i> = 0.009). Stratifying patients based on the median NLR into low- and high-risk groups revealed that the high-risk group exhibited a 1.324-fold increased risk of death compared to the low-risk group (HR = 1.324, 95% CI 1.069–1.640, <i>p</i> = 0.010). Subgroup analysis indicated that NLR independently predicted prognosis specifically in the invasive breast cancer subgroup (<i>p</i> = 0.002).</p> Conclusion <p>NLR emerges as a simple and accessible prognostic indicator in newly diagnosed patients with leptomeningeal metastasis stemming from solid tumors.</p>