Aim: International research has only rarely examined the functioning of families experiencing chronic illness and the perception of nurses towards involving families in patient care. This has also been the case in Denmark. To undertake this kind of research, carefully translated questionnaires are needed. The purpose of this study was therefore to translate the Ice Expressive Family Functioning (ICE-EFFQ) and the Ice Family Perceived Support (ICE-FPSQ) into Danish, and to test the validity and reliability of the Danish versions. Methods: The study had a cross-sectional design. The questionnaires were translated into Danish using forward-backward translation. Then, they were tested empirically among adult patients with chronic diseases and their family members in three different settings. A total of 81 patients were included in the testing of ICE-EFFQ and 70 patients were included in the testing of ICE-FPSQ. Internal consistency reliability was assessed followed by confirmatory factor analysis. Results: Both questionnaires showed acceptable construct validity, reliability (Cronbach's alpha 0.93 and 0.94), internal consistency were confirmed, and there was good reproducibility (Cronbach's alpha 0.76 and 0.77). Furthermore, confirmatory factor analysis showed acceptable to good fit for both questionnaires. Conclusions: The ICE-EFFQ and the ICE-FPSQ were both found to be valid and reliable instruments to measure family functioning and perceived support among families experiencing chronic illness in a Danish context.