OBJECTIVES: To assess available data on the numbers of technology- dependent children living at home in the UK and estimate the costs of caring for them. DESIGN: Data were obtained from all known secondary sources, including surveys of children with specific conditions known to specialist paediatric departments and the database of applicants to the Family Fund Trust. The costs of all services received by three hypothetical exemplar ‘case study’ children were calculated. RESULTS: All existing sources of data have some shortcomings. Taking these shortcomings into account, it is estimated that there may be up to 6000 technology-dependent children living at home. They appear to be disproportionately young and may be distributed unevenly between different regions of the UK. The total service costs of caring for each child will vary according to the types of technologies involved and local patterns of services, but may be as high as 150,000 pounds sterling a year. CONCLUSIONS: Because of the very high costs of services, routine information on the numbers of technology-dependent children discharged home is urgently needed. This should include details of the duration of technology dependence and the local area to which the child is discharged. New opportunities for joint service planning and purchasing should improve the co-ordination of services for these children.