Firearm homicide and microterritorial concentration of lethal violence in Lima-Callao, Peru, 2018-2025.

BACKGROUND: Homicide is an important injury prevention challenge in Latin American cities, but metropolitan trends can mask substantial local variation. Evidence from Peru remains limited, particularly on whether recent increases in homicide have been driven by firearm violence and concentrated within urban microterritories. METHODS: We conducted a population-based ecological study of homicide mortality in the Lima-Callao metropolitan area using Peru's National Death Information System, covering 2018 to 2025. We describe annual homicide counts and rates overall and by mechanism, distinguishing firearm from non-firearm homicide. For district-level spatial analyses, the study period was grouped into three phases (pre-pandemic, pandemic/recovery and post-pandemic) to improve stability of estimates. District rates were mapped, smoothed using empirical Bayes methods and analysed using global Moran's I and Local Indicators of Spatial Association. RESULTS: A total of 5602 homicides were recorded between 2018 and 2025. The homicide rate rose from 3.51 per 100 000 population in 2018 to 8.23 in 2024 and remained elevated at 8.37 in 2025. Firearm homicide accounted for 69.3% of all deaths and increased from 54.5% of homicides in 2018 to 78.4% in 2025. District-level analyses showed concentration of homicide in Callao and adjacent western districts, with firearm clustering more pronounced early in the study period but not persistent across phases. CONCLUSIONS: The recent rise in homicide in Lima-Callao was increasingly firearm-driven and concentrated within a small number of metropolitan microterritories. These findings support geographically targeted and firearm-oriented prevention strategies and highlight the value of routine small-area surveillance for urban violence prevention.