BACKGROUND: Hospital boards have statutory responsibility for upholding the quality of care in their organisations. International research on quality in hospitals resulted in a research-based guide to help senior hospital leaders develop and implement quality improvement (QI) strategies, the QUASER Guide. Previous research has established a link between board practices and quality of care; however, to our knowledge, no board-level intervention has been evaluated in relation to its costs and consequences. The aim of this research was to evaluate these impacts when the QUASER Guide was implemented in an organisational development intervention (iQUASER). METHODS: We conducted a 'before and after' cost-consequences analysis (CCA), as part of a mixed methods evaluation. The analysis combined qualitative data collected from 66 interviews, 60 hours of board meeting observations and documents from 15 healthcare organisations, of which 6 took part on iQUASER, and included direct and opportunity costs associated with the intervention. The consequences focused on the development of an organisation-wide QI strategy, progress on addressing 8 dimensions of QI (the QUASER challenges), how organisations compared to benchmarks, engagement with the intervention and progress in the implementation of a QI project. RESULTS: We found that participating organisations made greater progress in developing an organisation-wide QI strategy and became more similar to the high-performing benchmark than the comparators. However, progress in addressing all 8 QUASER challenges was only observed in one organisation. Stronger engagement with the intervention was associated with the implementation of a QI project. On average, iQUASER costed £23 496 per participating organisation, of which approximately 44% were staff time costs. Organisations that engaged less with the intervention had lower than average costs (£21 267 per organisation), but also failed to implement an organisation-wide QI project. CONCLUSION: We found a positive association between level of engagement with the intervention, development of an organisation-wide QI strategy and the implementation of an organisation-wide QI project. Support from the board, particularly the chair and chief executive, for participation in the intervention, is important for organisations to accrue most benefit. A board-level intervention for QI, such as iQUASER, is relatively inexpensive as a proportion of an organisation's budget.