PURPOSE: Recent studies have demonstrated that various diseases states (e.g., schizophrenia, Alzheimer's disease) and events (e.g., a stroke) alter a person's perception of their physical and mental status. Most often this involves alterations in a person's metacognitive capabilities, and this can question the conceptual model of quality of life (QoL) based on a "perspectivist" approach. METHODS: Using the example of schizophrenia, we applied a philosophical model, developed by Griffin, to deal with this potential threat to the validity of QoL assessment. RESULTS: Patients with schizophrenia are at risk for being impaired in their ability to assess their QoL. We hypothesise that metacognition (i.e., the ability to attribute mental states in terms of beliefs and goals to one's self and others) is a formal condition to assess QoL. This particular skill is important because self-reflection is necessary for making a qualitative judgment. A link between this psychological concept and the philosophical concept of reflexivity may be established. We propose a conceptual approach to QoL that takes into account the patient's reflexivity. This approach is derived from Griffin's theory based on the list of "prudential values" and the satisfaction of the informed desires of the individual. CONCLUSION: The ability of patients to evaluate and value their life should be considered to enrich the concept of QoL. The approach derived from Griffin's theory might constitute a new avenue for QoL research.