Children in care who experience frequent placement changes face an increased risk of negative mental health outcomes. Emerging evidence suggests a bidirectional relationship, where placement instability can both predict and result from mental health difficulties. Understanding the strength and direction of this relationship is crucial for informing policy and practice, yet UK-based evidence remains unconsolidated.

To conduct the first systematic review and meta-analysis examining the relationship between placement instability and mental health in the UK care system.

This review was prospectively registered on the International Prospective Register of Systematic Reviews (PROSPERO; CRD42024493617). We searched five databases (up to August 2024) for peer-reviewed UK studies that included a care-experienced sample, measured placement (in)stability, measured mental health, and quantitatively examined the relationship between placement instability and mental health. A random-effects meta-analysis was conducted, and study quality was assessed using the Newcastle–Ottawa Scale.

Fifteen studies (N = 6905) were included, with twelve studies (n = 5536) contributing to the meta-analysis. Children with unstable placements were more than twice as likely to experience mental health difficulties compared to those with stable placements (odds ratio 2.07, 95% CI 1.65–2.59). However, evidence on the causal direction of this relationship was limited.

Placement instability doubles the risk of mental health difficulties for care-experienced children, who already face elevated rates of mental disorders. Further research is urgently needed to clarify the bidirectional nature of this relationship and guide targeted intervention. Meanwhile, policymakers should prioritise collaborations between mental health services and local authorities to prevent the cycle of instability and mental health deterioration.