The 2006 São Paulo violence outbreak began on the night of May 12, 2006 in São Paulo, Brazil, the largest city in South America. It was among the worst outbreaks of violence in recorded Brazilian history (and has been called the worst) and was directed against security forces and a few civilian targets. By May 14 the attacks had spread to other Brazilian states including Paraná, Mato Grosso do Sul, Minas Gerais and Bahia (this without direct links to the PCC criminal organisation).

The violence began after forty São Paulo police officers were killed by gang violence. Subsequently, the police officers sought to find the gang members behind the criminal acts. In the process, a violent situation arose, creating a clash between law enforcement officials and criminals and taking the lives of over 150 people.

The wave of violence, amongst the worst in Brazil's history, received broad national and international media coverage, and this fact allied to the lack of information from the São Paulo state government caused mass panic among the population. The state governor, Cláudio Lembo, was harshly criticized by the press for the slow response to the violence, for the absence of communication between the security forces, for the lack of information, to the press and the general public, and for poor management of the crisis.