Despite similar post-migration adversities amongst comparison groups, findings suggest an independent adverse impact of detention on asylum seekers' mental health, with the magnitude of the effect sizes lying in an important clinical range. These effects persisted beyond release into the community. While based on limited evidence, this review supports concerns regarding the detrimental impact of detention on the mental health of already traumatised asylum seekers. Further research is warranted to comprehensively explore these effects. Detention of asylum seekers, already grappling with significant trauma, appears to exacerbate mental health challenges. Policymakers and practitioners should consider these findings in shaping immigration and asylum policies, with a focus on minimising harm to vulnerable populations.