Objective: This study systematically summarizes the evidence of all observational studies investigating the relation between accumulation of adverse life events and measures of overweight in children <18 years. Methods: MEDLINE, Embase, PsycINFO, and CINAHL were systematically searched (last search date 18 February 2015). The Newcastle-Ottawa Scale was used for methodological quality assessment. Study estimates were pooled using a random-effects model, and sources of heterogeneity were explored (PROSPERO registration number CRD42014014927). Results: Eighteen articles were included, containing five longitudinal (n = 6,361) and fourteen cross-sectional and case-control study results (n = 52,318). The pooled estimate of the longitudinal studies showed that accumulation of adverse life events is positively related to childhood overweight measures (OR [95% CI] = 1.12 [1.01-1.25]). Cross-sectional and case-control study results were heterogeneous. Subgroup analyses showed that cross-sectional and case-control studies using a continuous adverse events measure, studies using a continuous overweight measure, and studies in children >6-12 years also generated positive pooled estimates, while the pooled estimate of studies assessing recent adverse events (past 2 years) was indicative of no relation with overweight. Conclusions: Accumulation of adverse life events and childhood overweight measures are positively associated. However, increases in overweight measures in response to adverse childhood events do not seem to occur instantaneously.