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.