Background and objectives: Services have variable practices for identifying and providing interventions for ‘severe attachment problems’ (disorganised attachment patterns and attachment disorders). Several government reports have highlighted the need for better parenting interventions in at-risk groups. This report was commissioned to evaluate the clinical effectiveness and cost-effectiveness of parenting interventions for children with severe attachment problems (the main review). One supplementary review explored the evaluation of assessment tools and a second reviewed 10-year outcome data to better inform health economic aspects of the main review. Data sources: A total of 29 electronic databases were searched with additional mechanisms for identifying a wide pool of references using the Cochrane methodology. Examples of databases searched include PsycINFO (1806 to January week 1, 2012), MEDLINE and MEDLINE In-Process & Other Non-Indexed Citations (1946 to December week 4, 2011) and EMBASE (1974 to week 1, 2012). Searches were carried out between 6 and 12 January 2012. Review methods: Papers identified were screened and data were extracted by two independent reviewers, with disagreements arbitrated by a third independent reviewer. Quality assessment tools were used, including quality assessment of diagnostic accuracy studies – version 2 and the Cochrane risk of bias tool. Meta-analysis of randomised controlled trials (RCTs) of parenting interventions was undertaken. A health economics analysis was conducted. Results: The initial search returned 10,167 citations. This yielded 29 RCTs in the main review of parenting interventions to improve attachment patterns, and one involving children with reactive attachment disorder. A meta-analysis of eight studies seeking to improve outcome in at-risk populations showed statistically significant improvement in disorganised attachment. The interventions saw less disorganised attachment at outcome than the control (odds ratio 0.47, 95% confidence interval 0.34 to 0.65; p < 0.00001). Much of this focused around interventions improving maternal sensitivity, with or without video feedback. In our first supplementary review, 35 papers evaluated an attachment assessment tool demonstrating validity or psychometric data. Only five reported test–retest data. Twenty-six studies reported inter-rater reliability, with 24 reporting a level of 0.7 or above. Cronbach’s alphas were reported in 12 studies for the comparative tests (11 with α < 0.7) and four studies for the reference tests (four with α > 0.7). Three carried out concurrent validity comparing the Strange Situation Procedure (SSP) with another assessment tool. These had good sensitivity but poor specificity. The Disturbances of Attachment Interview had good sensitivity and specificity with the research diagnostic criteria (RDC) for attachment disorders. In our supplementary review of 10-year outcomes in cohorts using a baseline reference standard, two studies were found with disorganised attachment at baseline, with one finding raised psychopathology in adolescence. Budget impact analysis of costs was estimated because a decision model could not be justifiably populated. This, alongside other findings, informed research priorities. Limitations: There are relatively few UK-based clinical trials. A 10-year follow-up, while necessary for our health economists for long-term sequelae, yielded a limited number of papers. Conclusions: Maternal sensitivity interventions show good outcomes in at-risk populations, but require further research with complex children. The SSP and RDC for attachment disorders remain the reference standards for identification until more concurrent and predictive validity research is conducted. A birth cohort with sequential attachment measures and outcomes across different domains is recommended with further, methodologically sound randomised controlled intervention trials. The main area identified for future work was a need for good-quality RCTs in at-risk groups such as those enterifoster care or adoption. Study registration: This study is registered as PROSPERO CRD42011001395. Funding: The National Institute for Health Research Health Technology Assessment programme.