The Arbaeen pilgrimage is one of the world’s largest annually recurring religious mass gatherings, drawing multi-million cross-border participation to Karbala, Iraq. Long-distance walking, open borders, dense communal shelters (Mawkibs), and a largely volunteer-driven service ecosystem create a risk profile that differs from shorter, centralized events such as the Hajj. This narrative review synthesized the Arbaeen health literature (33 Arbaeen-specific core studies) and a focused comparative set from Hajj and broader mass-gathering medicine (7 studies), yielding 40 empirical studies in total. Evidence was synthesized across four domains: (A) respiratory and other communicable infections; (B) non-communicable diseases (NCDs) and trauma; (C) health-system preparedness and service delivery; and (D) environmental, climate, and WASH risks (including food/water safety and zoonotic hazards). Respiratory and gastrointestinal syndromes account for much of frontline clinical volume, whereas severe morbidity and mortality are more consistently driven by cardiovascular emergencies and traffic- or exertion-related injuries. Recurrent constraints include surge-capacity saturation along routes and border crossings, heterogeneous clinical governance across volunteer providers, and limited interoperability of surveillance and operational data. Preparedness should shift from episodic response toward an integrated prevention-and-resilience model combining real-time syndromic and environmental monitoring, standardized WASH controls, route-aware trauma/NCD readiness, and cross-border coordination, supported by a governed de-identified data infrastructure for year-to-year learning.