The aim of this prospective study was to identify the number of people with a possible learning disability suspected of having committed a criminal offence who were taken into police custody during a defined period of time. Between 18 January 1993 and 18 March 1993 992 people were taken into custody at Parkside Police Station, Cambridge, of whom 251 (25.3%) were screened by the custody officer using a brief questionnaire to ascertain the presence or absence of reading and writing difficulties and to see if they had received extra help at school of if they had attended a special needs school. Information on age, sex, suspected offence, disposal, if a solicitor assisted and incidence of homelessness was gathered from the custody reports. Eleven (4.4%) subjects screened had attended schools for children with moderate learning difficulties, while one (0.4%) suspect reported having attended a school for children with severe learning difficulties. A further 26 (10.4%) had attended schools for children with emotional or behavioural difficulties or a learning support unit within a mainstream school. Those detained who had attended a special needs school for children with learning difficulties were all male. They had a mean age of 23.0 years (SD = 5.0) compared to the mean age of all subjects of 26.5 years (SD = 11.6). They were more likely to have been suspected of having committed acquisitive offences than people who attended mainstream schools. In addition, they were more likely to be remanded in custody, or to be bailed, prior to appearing in court, in contrast with those from mainstream schools who were much more likely to be cautioned. Three (25%) of those who attended schools for children with learning difficulties had the assistance of a solicitor while in police detention. Two (16.7%) of those suspects who had attended a school for children with learning difficulties were homeless compared to 19 (8.0%) homeless suspects who had attended mainstream schools. These findings need to be considered when planning services for offenders. Existing or planned court diversion schemes should consider suspects with learning disabilities as well as those with other mental disorders. Health, probation and social services will be required if people with learning disabilities are to be diverted from the criminal justice system and the prison service should consider how to support a potentially vulnerable group if they are detained prior to trial or receive prison sentences.