BACKGROUND: The DIAMOND Project (Depression Is A MANageable Disorder), a nonrandomized controlled effectiveness trial, was intended to improve the long-term management of depression in primary care medical clinics. The project tested whether a quality improvement (QI) intervention could implement a systems approach-so that there would be more reliable and effective monitoring of patients with depression, leading to better outcomes. THE QUALITATIVE STUDY: A study was conducted in 1998-2000 to determine why a quality improvement intervention to improve depression care did not have a significant impact. Data consisted of detailed notes from observations of 12 project-related events (for example, team meetings and presentations) and open-ended interviews with a purposive sampling of 17 key informants. Thematic analytic methods were used to identify themes in the contextual data. PRINCIPAL FINDINGS: Overall, the project implementation was very limited. Five themes emerged: (1) The project received only lukewarm support from clinic and medical group leadership. (2) Clinicians did not perceive an urgent need for the new care system, and therefore there was a lack of impetus to change. (3) The improvement initiative was perceived as too complex by the physicians. (4) There was an inherent disconnect between the commitment of the improvement team and the unresponsiveness of most other clinic staff. (5) The doctor focus in clinic culture created a catch-22 dilemma-the involvement and noninvolvement of physicians were both problematic. CONCLUSION: Problems in both predisposing and enabling factors accounted for the ultimate failure of the DIAMOND quality improvement effort.