Aims and objectives: To assess the impact of family health conversations (FamHC) as a supplement to conventional care on health-related quality of life (HRQoL), family functioning (FFSS) and family hardiness or resilience (FHI) 4 and 14 weeks postoperatively among patients with glioblastoma multiforme and their family members. Background: There is a lack of knowledge about the efficiency of FamHC among families experiencing glioblastoma multiforme. Design: A quasi-experimental pre- and post-test design adhering to the STROBE (Strengthening the reporting of observational studies in epidemiology) guidelines for case–control studies. Patients and family members were included consecutively in the pretest period from November 2013–December 2014 for the control group (offered traditional care only), and in the post-test period from January 2015–December 2015 for the intervention group (offered traditional care and FamHC). For both groups, 4 and 14 weeks postoperative measurement were obtained. Methods: Differences in outcomes were assessed using a difference-in-difference regression analysis approach measuring difference across pre and post groups and across 4 and 14 weeks measurements. Results: The study does not reveal significant effects of FamHC (all p-values larger than 0.05) as measured by the three instruments WHOQOL-BREF, FFSS and FHI. Conclusions: The present study was not able to show significant effects of FamHC. However, it cannot be left out that the intervention might be helpful and supportive at a later state of the illness trajectory. Relevance for clinical practice: The study adds to the growing evidence-based knowledge on FamHC by questioning their potential use in different cultural contexts among families experiencing critical illness. Oncological nurses need to adapt this information to support their daily care for the patients and their close relatives. For future studies, it is recommended that the families themselves choose when the conversations should take place during the course of the illness.