This multiple case study evaluates four quality improvement collaboratives (QICs) in long-term mental health care focusing on social psychiatric care, recovery oriented care, social participation and somatic co-morbidity of psychiatric patients. The aim is to explore (1) effectiveness in terms of objective outcome indicators and impact of changes as perceived by team members; and (2) associations between collaborative-, organizational- and team-level factors and perceived effectiveness. Most objective outcomes, such as health, loneliness and clients' problem areas, showed significant improvement. Because of the diversity in content no single measure for objective effectiveness could be computed across the four collaboratives. Perceived effectiveness of team members was used as an indicator of the overall impact. In all, 55 of the 94 participating team leaders and 117 remaining team members completed a written survey at the end of each quality improvement collaborative. Multilevel regression analyses indicated that innovation attributes, appropriate measures, usable data collection tools and an innovative team culture could explain variation in perceived effectiveness. In conclusion, overall positive changes for clients were realized as demonstrated by objective outcomes and team members' perceptions of improvements in care processes. The results supported the notion that a layered approach is necessary to achieve improvements in quality of care.