The quality of life in persons with severe and persistent mental illness is often poor. Most treatment programmes have the goal of increasing quality of life. Unfortunately, existing methods to assess quality of life are cumbersome and oriented towards research rather than clinical settings. This study describes preliminary steps in the development, testing and application of a new patient focused index for measuring quality of life in persons with severe mental illness. The Quality of Life Index for Mental Health (QLI-MH) differs from existing instruments in that it is based on an easy to use, self-administered questionnaire that assesses nine separate domains that together encompass quality of life. Each domain can be individually weighted depending on its relative importance to the patient. Different parts of the instrument solicit information from the patient, the primary clinician, and, when available, the family. The instrument and its scoring system address limitations of previous approaches to quality of life measurement.