Background:Advance care planning supports patients to reflect on and discuss preferences for future treatment and care. Studies of the impact of advance care planning on healthcare use and healthcare costs are scarce.Aim:To determine the impact on healthcare use and costs of an advance care planning intervention across six European countries.Design:Cluster-randomised trial, registered as ISRCTN63110516, of advance care planning conversations supported by certified facilitators.Setting/participants:Patients with advanced lung or colorectal cancer from 23 hospitals in Belgium, Denmark, Italy, the Netherlands, Slovenia and the UK. Data on healthcare use were collected from hospital medical files during 12 months after inclusion.Results:Patients with a good performance status were underrepresented in the intervention group (p< 0.001). Intervention and control patients spent on average 9 versus 8 days in hospital (p = 0.07) and the average number of X-rays was 1.9 in both groups. Fewer intervention than control patients received systemic cancer treatment; 79% versus 89%, respectively (p< 0.001). Total average costs of hospital care during 12 months follow-up were €32,700 for intervention versus €40,700 for control patients (p = 0.04 with bootstrap analyses). Multivariable multilevel models showed that lower average costs of care in the intervention group related to differences between study groups in country, religion and WHO-status. No effect of the intervention on differences in costs between study groups was observed (p = 0.3).Conclusions:Lower care costs as observed in the intervention group were mainly related to patients’ characteristics. A definite impact of the intervention itself could not be established.