BACKGROUND: Immediate breast reconstruction after mastectomy can improve the quality of life for women with breast cancer and rates are increasing. Long-term inpatient costs of care were estimated to understand the impact of different immediate breast reconstruction procedures on healthcare expenditure. METHODS: Hospital Episode Statistics Admitted Patient Care data were used to identify women undergoing unilateral mastectomy and immediate breast reconstruction in English National Health Service hospitals (1 April 2009 to 31 March 2015) and any subsequent procedures performed to revise, replace, or complete the breast reconstruction. Costs were assigned to Hospital Episode Statistics Admitted Patient Care data using the Healthcare Resource Group 2020/21 National Costs Grouper. Generalized linear models were used to estimate mean cumulative costs for five immediate breast reconstruction procedures over 3 and 8 years, adjusting for covariates (age/ethnicity/deprivation). RESULTS: A total of 16 890 women underwent mastectomy and immediate breast reconstruction: implant (5192; 30.7 per cent), expander (2826; 16.7 per cent), autologous latissimus dorsi flap (2372; 14.0 per cent), latissimus dorsi flap with expander/implant (3109; 18.4 per cent), and abdominal free-flap reconstruction (3391; 20.1 per cent). The mean (95 per cent c.i.) cumulative cost was lowest for latissimus dorsi flap with expander/implant reconstruction (€20 103 (€19 582 to €20 625)) over 3 years and highest for abdominal free-flap reconstruction (€27 560 (€27 037 to €28 083)). Over 8 years, expander (€29 140 (€27 659 to €30 621)) and latissimus dorsi flap with expander/implant (€29 312 (€27 622 to €31 003)) reconstructions were the least expensive, while abdominal free-flap reconstruction (€34 536 (€32 958 to €36 113)) remained the most expensive, despite having lower costs for revisions and secondary reconstructions. This was driven primarily by the cost of the index procedure (€5435 (expander reconstruction) to €15 106 (abdominal free-flap reconstruction)). CONCLUSION: Hospital Episode Statistics Admitted Patient Care Healthcare Resource Group data provided a comprehensive longitudinal cost assessment of secondary care. Although abdominal free-flap reconstruction was the most expensive option, higher costs of the index procedure need to be balanced against ongoing long-term costs of revisions/secondary reconstructions, which are higher after implant-based procedures.