Provision of a healing environment could help arrive at better healthcare outcomes. Healing environments that enjoy natural daylight have a positive impact on the health and well-being of patients and medical staff. They contribute to the achievement of shorter lengths of stay, reduction of stress and increase of patients and staff satisfaction. Several studies have emphasized the positive role of daylighting as one of the most influential factors for creating successful healing environments in healthcare facilities. This is especially important in patient rooms, which represent the largest component of hospital buildings. Provision of adequate daylighting is quiet a challenging task in desert locations which are typically characterized by year-long clear skies. External sun-breakers are typically used in these locations to control solar penetration, thus improving illuminance distribution and decreasing visual discomfort. This study aims at defining the main characteristics of the sun-breakers that could be used to control solar access into hospital patient rooms under clear-sky conditions. The study addressed two common patient room designs: inboard bathroom design and outboard bathroom design. The tested rooms had three equidistant sun-breakers that are externally fixed in front of a window facing south in Cairo, Egypt. The focus was on the impact of the sun-breakers' cut off angle and the corresponding tilt angle on year-round illuminance distribution and visual discomfort. The main goal was to ensure adequate daylighting performance without discomfort glare inside these rooms. Parametric simulation runs were performed using Grasshopper, Diva-for-Rhino, and SpeedSim-for-DIVA, plug-ins for Rhinoceros modeling software to interface with the simulation engines Radiance and Daysim software. The outcomes of this study identified the range of sun-breaker cut off angles and their corresponding tilt angles which produced adequate daylighting performance for the two patient room types at different window to wall ratios. In general, the number of accepted sun-breaker cases increased with higher window to wall ratios for both patient room designs. It was noted that a wider range of accepted tilt angles was identified for the patient rooms having inboard bathrooms. Both the inboard and outboard bathroom designs had the same range of accepted cut off angles. It was observed that efficient daylighting performance was achieved in all tested WWRs for the two patient room layouts with cut off angles between 50 and 54 with the wall. Moreover, horizontal sun-breakers achieved successful results in all tested WWRs for the two patient room layouts. It was also noted that the cut off angles were more influential in providing adequate daylighting performance in comparison with tilt angles. (C) 2017 Elsevier Ltd. All rights reserved.