BACKGROUND: Introduction of crisis resolution/home treatment teams has been associated with a reduction in hospital admissions in trials. Between 2001 and 2004 there was a rapid expansion in the numbers of these teams in England. AIMS: To examine whether national implementation of these teams was associated with comparable reductions in admissions. METHOD: Observational study using routine data covering working age adult patients in 229 of the 303 local health areas in England from 1998/9 to 2003/4. RESULTS: Admissions fell generally throughout the period, particularly for younger working age adults. Introduction of crisis resolution teams was associated with greater reductions for older working age women (35-64 years); teams always on call were associated with additional reductions for older men and younger women. By the end of the study admissions had fallen by 10% more in the 34 areas with crisis resolution teams in place since 2001, and by 23% more in the 12 of these on call around the clock than in the 130 areas without such teams by 2003/4. Reductions in bed use were smaller. Introduction of assertive outreach teams was not associated with overall reductions in admissions. CONCLUSIONS: Introduction of crisis resolution teams has been associated with reductions in admissions.