The objective of this study was to describe the risks and human health outcomes associated with attendance at the Moulay Abdellah Amghar moussem (a pre-planned mass gathering attracting more than 360 000 participants) for the purposes of public health prevention, planning, preparedness and response. We performed an environmental health risk assessment and retrospectively reviewed local health centre records before, during and after the event. In addition, standardized interviews with key stakeholders were performed to qualitatively evaluate local public health preparedness and response capacities. During the event, average daily health centre visits increased 5-fold. The sex ratio of health-care visits changed significantly from an average of 1.81 femalemale visits per day to 1.21. The proportion of injuries varied from an average of 3.7% pre- and post-event to 14.8% (P < 0.01) during the event. A significant increase in digestive diseases was also observed during the event. Recommendations include increasing accessibility to free sanitation and hygiene facilities and improving health communications concerning hand washing and food and water safety.