Background: It was hypothesised that the introduction of tools that allow clinicians to assess patients' needs and to negotiate treatment (Cumulative Needs for Care Monitor; CNCM), would be associated with global outcome improvements in patients diagnosed with severe mental illness. Methods: The CNCM was introduced in one region in South Limburg (the Netherlands) in 1998 (REGION-1998) and in the rest of South Limburg in 2004 (REGION-2004). By comparing these two regions, changes after the introduction of the CNCM could be assessed (between-region comparison). In addition, a pre-post within-patient comparison was conducted in both regions. Results: The within-patient comparison revealed that global outcomes of psychopathology and impairment improved in the first 3-5 years after the introduction of the CNCM. The between-region comparison revealed an improvement in global psychopathology but not in global impairment in REGION-2004 after 2004, while there was no such improvement in REGION-1998. Conclusion: Systematic clinical monitoring of individual severe mental illness patients, in combination with provision of feedback, is associated with global improvement in psychopathology. More research is needed to determine the degree to which this association reflects a causal effect.