There is an extensive body of research into trends in use of the 1983 mental health act (MHA) and crisis resolution and home treatment (CRHT) teams, but only one study has examined the relationship between the two. The introduction of these teams led to the belief that use of the MHA would decrease as more people with mental health problems were treated in their own environment when in crisis and at risk of admission to hospital. However, in one county authority in south- east England, the numbers of MHA assessments continued to rise after the introduction of the CRHT team. To investigate this pattern, we examined a random sample of MHA assessments conducted in the catchment area of the CRHT team both in and out of office hours from two time periods- one before and one after the introduction of the CRHT team. The presence of the team was associated with a significant increase in the use of section 2 MHA, although the use of section 3 MHA decreased. To explore these findings, we held focus groups to obtain the views influenced decisions. We found that the role of the Approved Social Worker (ASW) was poorly understood in the new CRHT team and that communication between it and the ASWs was disjointed. Integration of ASWs into predominantly medical CRHT teams will assist joint decision making about use of the MHA and may help to reduce unnecessary compulsory hospital admissions.