Background Given the frequency with which families change residences, the effects of childhood relocations have gained increasing research attention. Many researchers have demonstrated that childhood relocations are associated with a variety of adverse outcomes. However, drawing strong causal claims remains problematic due to uncontrolled confounding factors. Methods We utilized longitudinal, population-based Swedish registers to generate a nationally representative sample of offspring born 1983–1997 (n=1,510,463). Using Cox regression and logistic regression, we examined the risk for numerous adverse outcomes after childhood relocation while controlling for measured covariates. To account for unmeasured genetic and environmental confounds, we also compared differentially exposed cousins and siblings. Results In the cohort baseline model, each annual relocation was associated with risk for the adverse outcomes, including suicide attempt (HR=1.19; 95% CI, 1.19–1.20). However, when accounting for offspring and parental covariates (e.g., HR=1.08; 95% CI, 1.07–1.09), as well as genetic and environmental confounds shared by cousins (HR=1.07; 95% CI, 1.05–1.09) and siblings (e.g., HR=1.00; 95% CI, 0.97–1.04), the risk for suicide attempt attenuated. We found a commensurate pattern of results for severe mental illness, substance abuse, criminal convictions, and low academic achievement. Conclusions Previous research may have overemphasized the independent association between relocations and later adverse outcomes. The results suggest that the association between childhood relocations and suicide attempt, psychiatric problems, and low academic achievement is partially explained by genetic and environmental confounds correlated with relocations. This study demonstrates the importance of using family-based, quasi-experimental designs to test plausible alternate hypotheses when examining causality.