Background The McGill Quality of Life Questionnaire - Expanded (MQOL-E) and the Quality of Life in Life-Threatening Illness-Family Carer/Caregiver version (QOLLTI-F) are developed for use with patients facing the end of life and their family carers, respectively. They are also developed for possible use as companion instruments. Contemporary measurement validity theory places emphasis on response processes, i.e. what people feel and think when responding to items. Response processes may be affected when measurement instruments are translated and adapted for use in different cultures. The aim of this study was to translate and examine content validity and response processes during completion of MQOL-E and QOLLTI-F version 2 (v2) among Swedish patients with life-threatening illness and their family carers. Methods The study was conducted in two stages (I) translation and adaptation (II) examination of content validity and response processes using cognitive interviews with 15 patients and 9 family carers. Participants were recruited from the hemodialysis unit, heart clinic, lung clinic and specialized palliative care of a Swedish county hospital. Patients had life-threatening illness such as advanced heart failure, advanced chronic obstructive pulmonary disease, end-stage kidney disease or advanced cancer. Patients were outpatients, inpatients or receiving home care. Results Patients and family carers respectively believed that the items of the MQOL-E and QOLLTI-F v2 reflect relevant and important areas of their quality of life. Although some items needed more time for reflection, both instruments were considered easy to understand. Some changes were made to resolve issues of translation. Participants expressed that reflecting on their situation while answering questions was valuable and meaningful to them, and that responding was an opportunity to express feelings. Conclusions The results of response processes pertaining to the Swedish translations of both MQOL-E and QOLLTI-F v2 contribute evidence regarding content validity, linguistic equivalence and cultural appropriateness of the translated instruments. In addition, results show that the instruments may support conversations on matters of importance for quality of life between patients and/or family carers and health care professionals. Further research is needed to study the psychometric properties of Swedish translations.