In September 2015, Pope Francis visited Philadelphia, Pennsylvania, and led outdoor events over the course of 2 days. As a result, The Children’s Hospital of Philadelphia (CHOP) was faced with the challenge of planning for and responding to a mass gathering that was anticipated to be one of the largest in US history. As a result of unprecedented traffic restrictions, it was anticipated that patients, staff, and vendors would have severe challenges accessing the hospital, along with impaired communications from widespread cell phone service disruption. Previous mass gatherings have proven a need for early, detailed planning with multidisciplinary stakeholders, but little has been published on the impact of mass gatherings on area hospitals. This lack of data makes it difficult to predict the extent to which demand for hospital services would be increased and which services would be most affected. Early, coordinated planning allowed CHOP leaders to delegate responsibilities to those with specific expertise, prioritize needs, prevent duplication of efforts, and ensure engagement and accountability from key stakeholders. Emergency preparedness-led efforts including housing almost 1000 employees for 3 consecutive nights and assisting families with access allowed our hospital to maintain operations. The planning strategies shared here will provide emergency preparedness planners with a blueprint for future mass gathering preparedness. (Disaster Med Public Health Preparedness. 2017;11:267–276)