Aim: The primary objective of the IMPRESS study is to assess the causal effects of the IQM peer review on mortality in patients ventilated > 24 h. Secondary analyses are conducted for mortality in patients with myocardial infarction, stroke, COPD, pneumonia, and the procedural provision of a colorectal resection. This article provides a description of the study design and presents baseline results. Subjects and methods: Descriptive statistics for 231 included hospitals and patient characteristics. Results: Due to randomization, the treatment/control group hospitals were similar with respect to the mortality in patients ventilated > 24 h and other patient and hospital characteristics at baseline. Mortality was highest (lowest) in patients ventilated > 24 h (with colorectal resection). Conclusion: The IMPRESS study provides a unique opportunity to assess the impact of the IQM peer review on the mortality in patients ventilated > 24 h. The secondary, exploratory, and qualitative analyses are expected to provide insights on determinants of in-hospital mortality, structure and process quality, and the robustness of different approaches to risk adjustment of quality indicators.