Background: An increasing number of trials are stopped earlier than originally planned. It has been suggested that trials stopped pre-maturely overestimate the treatment effect. With the outlined observational study, we aim to simulate the results of stopping trials before they reach their planned sample size to assess the effects on mortality estimates. Methods and statistics: Based on 3 international, randomised clinical trials (RCTs) in critical care: Scandinavian Starch for Severe Sepsis and Septic Shock (6S) trial, the Transfusion Requirements in Septic Shock (TRISS) trial and the Stress Ulcer Prophylaxis in the Intensive Care Unit (SUP-ICU) trial, we will estimate relative risks with 95% confidence intervals for the primary outcome 90-day mortality after the inclusion of each individual patient in each RCT. This will be presented graphically with the primary outcome as a function of the number of included patients. Discussion: The outlined study will provide important knowledge about the effects of stopping critical care trials early. This may have important implications for patients, relatives, clinicians, researchers, guideline committee members and policy makers. Ethics and dissemination: We will use data from consenting patients enrolled in RCTs approved by the relevant ethical committees; this study requires no further permissions. We will report the results in accordance with the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) statement and submit the final approved manuscript to a peer-reviewed journal.