INTRODUCTION: It remains unclear whether changes in peripheral blood immune cells are distinct in suicidal ideation (SI) or suicidal behavior (SB) beyond depression. We systematically reviewed and meta-analyzed peripheral immune cell counts across samples with SI/SB and healthy controls or psychiatric patient populations. METHODS: MEDLINE, Embase, and PsycINFO databases were searched for articles published until 12th June 2023. Two reviewers independently selected the articles for inclusion, extracted data, and assessed the risk of bias using the Newcastle-Ottawa scale. A random effect model was used for meta-analysis on effect sizes measured as the standard mean difference in the immune cellular counts or their ratios with 95% confidence intervals across groups of samples with and without suicidal ideation or behavior. Heterogeneity between studies was measured by a restricted maximum-likelihood estimator for tau statistic and I2-statistic and tested by the Q test. Meta-regression was performed on age, gender, current-lifetime SI/SB, and the type of self-harming behavior (SI or SB). The study was registered with PROSPERO, CRD42023433089. RESULTS: We included 30 studies in the systematic review. Data from 19 studies were included in the meta-analyses, comprising 139 unique comparisons between 1973 persons with suicidal ideation or behaviors and 5537 comparison subjects and eleven immune cells or ratios. WBC and neutrophil counts were higher in individuals with SI/SB than in controls (SMD = 0.458; 95% CI = 0.367 - 0.548; p-value = < 0.001; I2= 0.002% and SMD = 0.581; 95% CI = 0.408 - 0.753; p < 0.001, respectively), signaling an inflammatory response. Notably, lymphocyte counts did not significantly differ. The neutrophil-to-lymphocyte ratio (NLR) showed a notable elevation in individuals with SI/SB (SMD = 0.695; 95% CI = 0.054 - 1.335; p-value = 0.033; I2 = 94.281%; Q test p-value = < 0.001). Comparisons among participants with and without SI/SB and depression revealed similar trends. Further, they showed increased NLR, monocyte-to-lymphocyte ratio (MLR), and platelet-to-lymphocyte ratio (PLR) in depressed individuals with SI/SB compared to those without SI/SB. CONCLUSIONS: A broad alteration in the peripheral immune cell populations and their ratios in SI/SB indicates accompanying immune activation or dysfunction. These changes were also evident in SI/SB among individuals with depression,suggesting immune involvement in SI/SB independent of depression.