Background: Koro syndrome is a culture-bound psychogenic condition characterized by acute anxiety involving perceived genital retraction accompanied by fear of imminent death. There remains a relative paucity of literature from sub-Saharan Africa, where such outbreaks are often linked to culturally embedded beliefs and accusations of genital theft, resulting in social unrest and violence. In April 2026, Tanzania experienced a sudden and widespread emergence of Koro-like symptoms across multiple geographically distinct regions. This case series aims to characterize the clinical features, sociocultural context, and public health consequences of this unprecedented event. Case presentations: We report over 30 cases identified across multiple geographically distinct regions. The majority of affected individuals were males aged 20–35 years, with only one female case documented. A consistent narrative emerged in which individuals believed that being touched on the shoulder triggered genital retraction. Protective behaviours included the use of improvised devices such as a safety pin attached to a rubber band, believed to prevent retraction. Individuals suspected of causing genital retraction were targeted by mobs and subjected to severe physical assaults, resulting in multiple injuries and fatalities. Conclusion: This first documented cluster of Koro-like syndrome in Tanzania highlights the potential for rapid community spread and escalation into interpersonal violence. These findings underscore the importance of integrated cultural, behavioural, and public health communication frameworks, and the need for further research to inform timely, coordinated public health and security responses.