BackgroundMillions of Iraqi pilgrims travel annually from the southern governorates to Karbala and pass through Thiqar, Muthana, and Diwania Governorates to join the Arbaeenia mass gathering event. During this event, participants are at high risk for diseases and death and stifle local health care resources. In addition, the mass gathering causes considerable burden on health facilities in the hosting localities.ObjectiveThis study aims to estimate the disease burden on health facilities caused by the pilgrims passing through Thiqar, Muthana, and Diwania Governorates en route to Karbala in Iraq.MethodsThis cross-sectional study was conducted on all health facilities in three governorates (Thiqar, Muthana, and Diwania) situated along the southern way to Karbala from Basra. The study started on December 11, 2014, and ended on December 24, 2014. The morbidity and mortality were collected from surveillance logbooks and death registers. Drug purchase data were obtained from the personnel in charge of the pharmacies. The study period was divided into three phases on the basis of the timing of the mass gathering event: pre-event, the event, and postevent.ResultsThere were 884,834 incidents reported during the study. The majority of incidents were reported during the event phase (95%) and were attended mostly at mobile clinics (77%). The average daily incidents during the pre-event, event, and postevent phases were 4300, 56,040, and 4548 incidents, respectively. Musculoskeletal disorders were the most common illness reported (55%). The average number of daily deaths was 43, 36, and 45 during the pre-event, event, and postevent, respectively, and these values did not differ significantly. Cardiovascular diseases (43.5%), injuries (29.8%), and respiratory illnesses (12%) were the leading causes of deaths. Approximately US $1.3 million was spent on drug purchases during this mass gathering in the three governorates.ConclusionsThe Arbaeenia mass gathering causes a tremendous disease and economic burden on governorates that pilgrims pass through to attend this mass gathering in Karbala. Although Iraq’s Ministry of Health is aware of the high burden of this mass gathering on the health facilities in these governorates, more work is needed to ensure quality services during the event.