Whilst the importance of community-based rehabilitation treatment programmes for people with acquired brain injury is increasingly recognised, there are as yet few well-validated outcome measures which take account both of the specific (participation-related) foci of treatment in this setting and of methodological constraints that make inpatient techniques difficult to use. There is rarely the opportunity for extended observation of clients' day-to-day functioning, nor is it usually possible to seek consensual judgements from a multidisciplinary team as with some of the well-established disability measures that are generally the instruments of choice in hospital settings. Attempts to import such instruments into community assessment rely on administration techniques (e.g. interview) which have not been adequately validated in most cases, and whose reliability and accuracy is unknown. An additional limitation is that many patients living in the community score at ceiling on these measures despite having significant difficulties in living independently or in resuming premorbid social activities and roles. The composition, client group,and clinical framework of the multidisciplinary RNRU Outreach Team is described to illustrate the requirements of assessment techniques in community rehabilitation. The team has been subjected to a randomised controlled treatment trial, necessitating the use of sensitive and reliable quantitative assessment measures which were applicable across a functionally heterogeneous group. In the absence of suitable existing measures, the BICRO-39 scales were developed and validated on a sample of 235 patients with acquired brain injury. Clients and/or their carers rate the client's functioning in various domains; the scales show good test-retest reliability, high agreement between clients and carers, and reasonable construct validity. Most of the subscales are sensitive to change over a period of community-based rehabilitation.