A conceptual model of adaptation to illness/treatment and quality of life in cancer and especially bone marrow transplant patients is presented. The process from the diagnosis of a life–threatening disease to adaptation to it is divided into five stages. This process starts with the initial stimuli (stressor) and the appraisal/perception of that as a threat (stage I), and continues with the reaction to the stressor, if it is perceived as a threat (stage II). This is the time that, if manipulation of the stressor with appropriate interventions occurs, prevention of ineffective coping and/or maladjustment to illness is possible. The third stage refers to the coping with the illness (adaptive or maladaptive coping), followed by the degree of adaptation to illness and satisfaction with daily life (quality of life). Depending on interventions applied at this stage, the outcome can be either adjustment to illness or maladjustment and low quality of life (final stage). In every stage of the process, certain physiological, psychological, social and developmental variables are important, and these are described, based on research findings. Assessment of these variables is necessary for more effective planning of care and application of nursing interventions. Such a model can provide a conceptual framework for the assessment and evaluation of quality of life in cancer/bone marrow transplant patients and can help health professionals, and nurses in particular, to develop their own assessment tools and plan care and/or interventions based on such a holistic assessment.