The objective of this study was to develop comprehensive guidelines for medical care during mass gatherings based on the experience of providing medical support during rave parties. Study design was a prospective, observational study of self-referred patients who reported to First Aid Stations (FASs) during Dutch rave parties. All users of medical care were registered on an existing standard questionnaire. Health problems were categorized as medical, trauma, psychological, or miscellaneous. Severity was assessed based on the Emergency Severity Index. Qualified nurses, paramedics, and doctors conducted the study after training in the use of the study questionnaire. Total number of visitors was reported by type of event. During the 2006-2010 study period, 7,089 persons presented to FASs for medical aid during rave parties. Most of the problems (91.1%) were categorized as medical or trauma, and classified as mild. The most common medical complaints were general unwell-being, nausea, dizziness, and vomiting. Contusions, strains and sprains, wounds, lacerations, and blisters were the most common traumas. A small portion (2.4%) of the emergency aid was classified as moderate (professional medical care required), including two cases (0.03%) that were considered life-threatening. Hospital admission occurred in 2.2% of the patients. Fewer than half of all patients presenting for aid were transported by ambulance. More than a quarter of all cases (27.4%) were related to recreational drugs. During a five-year field research period at rave dance parties, most presentations on-site for medical evaluation were for mild conditions. A medical team of six healthcare workers for every 10,000 rave party visitors is recommended. On-site medical staff should consist primarily of first aid providers, along with nurses who have event-specific training on advanced life support, event-specific injuries and incidents, health education related to self-care deficits, interventions for psychological distress, infection control, and disaster medicine. Protocols should be available for treating common injuries and other minor medical problems, and for registration, triage, environmental surveillance and catastrophe management and response.