Inflammation influences cancer development and progression. An elevated platelet to lymphocyte ratio (PLR), a marker of inflammation, has been linked to poor prognosis in several malignancies. Here, we quantify the prognostic impact of this biomarker. A systematic review of databases was conducted to identify publications exploring the association of blood PLR and overall survival (OS) in solid tumors. Data were pooled in a meta-analysis. Pooled HRs for OS by disease group and by PLR cutoff groups were computed and weighted using generic inverse-variance and random-effect modeling. Twenty studies comprising 12,754 patients were assessed. Cutoffs for PLR defining risk groups ranged from 150 to 300 and were dichotomous (12 studies; group 1) or split into three groups (<150/150-300/>300, 8 studies; group 2). Higher PLR was associated with significantly worse OS in group 1 HR = 1.87; 95% confidence interval (CI, 1.49-2.34); P < 0.001 and with a nonsignificant association in group 2 (HR per higher category = 1.21; 95%CI, 0.97-1.50; P = 0.10). The size of effect of PLR on OS was greater for metastatic disease (HRgroup 1 = 2.0; 95% CI, 1.6-2.7; HRgroup 2 = 1.6; 95% CI, 1.1-2.4) than for early-stage disease (HRgroup 1 = 1.5; 95% CI, 1.0-2.2; HRgroup 2 = 1.0; 95% CI, 0.8-1.3). A significant association was observed for colorectal, hepatocellular, gastroesophageal, ovarian, and pancreatic carcinoma in group 1 and for colorectal cancers in group 2. A high PLR is associated with worse OS in various solid tumors. Further research of its regulation and relevance in daily practice is warranted. PLR is a readily available and inexpensive biomarker with independent prognostic value in solid tumors.