question: BACKGROUND: Palliative care phases (stable, unstable, deteriorating, terminal and bereavement) are routinely used in Australia and the UK to describe the clinical situation of patients and their families and to evaluate the associated care plan. In addition, it serves as a benchmark developed by the Australian Palliative Care Outcome Collaboration (PCOC) and is used nationwide for comparisons between services. In Germany, the concept is not used consistently due to various translations. Furthermore, there is no nationwide systematic approach to routinely assess clinical outcomes in palliative care. The study aims to develop a German version of the palliative care phase definitions by adapting them culturally, and to examine the inter-rater reliability of the adjusted definitions with healthcare professionals. METHODS: Mixed-methods approach: Cognitive interview study using ‘think aloud’ and verbal probing techniques and a consecutive multi-center cross-sectional study with two clinicians independently assigning the phase definitions. Interviewees/participants were selected through convenience and purposive sampling in specialist palliative care inpatient units, advisory and community services and in three specialist palliative care units with doctors, nursing staff and allied health professionals. RESULTS: Fifteen interviews were conducted. Identified difficulties were: Some translated terms were 1) not self-explanatory (e.g. ‘family/carer’ or ‘care plan’) and (2) too limited to the medical dimension neglecting the holistic approach of palliative care. (3) Problems of comprehension regarding the concept in general occurred, e.g. in differentiating between the ‘unstable’ and ‘deteriorating’ phase. Inter-rater reliability was moderate (kappa = 0.44; 95% CI = 0.39–0.52). The assignment of the phase ‘deteriorating’ has caused the most difficulties. CONCLUSION: Overall, the adapted palliative care phases are suitable to use in the German specialist palliative care setting. However, the concept of the phases is not self-explanatory. To implement it nationwide for outcome measurement/benchmarking, it requires further education, on-the-job training and experience as well as the involvement of healthcare professionals in implementation process. For the use of international concepts in different healthcare systems, a deeper discussion and cultural adaptation is necessary besides the formal translation. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12904-021-00825-z.