Families, as a unit, play an important role in the process of making decisions about care for and with adult cancer patients. Families often step in as the patient's advocate and primary decision-maker as the patient's condition deteriorates. How well caregivers fulfill that role may depend on the level of congruence between the family members and the patient. Disagreements may jeopardize processes of decision-making and treatment choice. To facilitate the clinical assessment process and to provide a tool for research, we are designing an instrument that can validly and reliably assess the level of family discord concerning the treatment of late stage cancer as they consider participation in clinical trials, palliative care and salvage treatment such as chemotherapy designed to decrease tumor burden without hope of cure. Development of the instrument is a four step process to develop and test the instrument: (1) formative interviewing with lung cancer patients and their family caregivers to identify and develop a comprehensive list of domains and items; (2) refinement of the items' wording with a sample of 43 patients and 67 family caregivers; (3) testing the reduced item pool to determine statistical and content validity and reliability with an initial of sample of 42 patients and their primary caregivers; (4) examination of the 30-item scale's properties with 160 lung cancer patients and their primary caregivers.