An outbreak of Portuguese man-of-war (Physalia physalis - Linnaeus, 1758) envenoming in Southeastern Brazil.

Introduction: Portuguese man-of-war, Physalia physalis (Linnaeus, 1758), are cnidarians capable of discharging intracellular organelles filled with venom, resulting in severe envenomation in humans.

Methods: We report the clinical and therapeutic aspects of 331 accidents involving Portuguese man-of-war in an outbreak on the coast of the State of São Paulo, Brazil.

Results: The clinical manifestations of envenomation were rare and mild and mostly local, systemic reactions; there was a low rate of late complications.

Conclusions: The consequences of envenomation were of moderate severity, and first aid measures were effective in controlling the pain. Outbreaks of accidents involving Portuguese man-of-war occur periodically in the area without a clear explanation.