The Healthcare Commission has launched an investigation into the services provided by the NHS trust responsible for Broadmoor high-security psychiatric hospital.
The move follows concerns about how West London Mental Health NHS Trust handles serious incidents involving its patients, including self-harming.
The Commission will examine whether the trust takes appropriate action to prevent similar things happening again in the future.
Officials ruled that an investigation was necessary after making unannounced visits to several of the trust's sites on February 13.
The inquiry will look at how the trust responded to incidents and "near misses" from April 2005 to the present.
Nigel Ellis, the Commission's head of investigations, said: "We are not saying the services provided by the trust are unsafe.
"If we believed they were unsafe we would take immediate action. But we have a duty to patients to be certain that all necessary systems are in place to manage risks.
"We are pleased to have the full co-operation of the trust in our work and will report back fully and publicly in due course, making recommendations to improve services if necessary."
West London Mental Health NHS Trust employs 3,800 staff at 32 sites to provide care for up to 18,000 patients in the London boroughs of Ealing, Hounslow, Hammersmith and Fulham.
It is also responsible for high security services at Broadmoor, where notorious criminals including Yorkshire Ripper Peter Sutcliffe are held, although the Commission said this was "not the main focus" of its investigation.
