Historically in hemophilia, outcome measures have not been collected systematically. Hence, there are insufficient clearly defined, evidence-based measures that can be applied consistently across hemophilia trials. This review focuses on some key challenges to evaluating patient outcomes and performing trials identified by experts at the Fourth and Fifth Zurich Haemophilia Forums. As procedures appear inconsistent across Europe, guidelines require modification to be more appropriate and/or realistically achievable. The outcome measures utilized, and the timing of their collection, should also be standardized, and more objective measures used where feasible. Implementation of outcome measures could be refined through greater understanding of patient heterogeneity, and tailored to differentiate between hemophilia- and aging-related disease effects. Furthermore, robust outcome measures that can also inform health-economic decisions are increasingly needed. Lastly, as patient recruitment poses a challenge, the panel proposed a call for action to motivate physicians and patients to participate in clinical trials.