The mental health trust responsible for high security hospital Broadmoor is being investigated after fears were raised over its patient safety processes.
The Healthcare Commission is investigating the way West London Mental Health trust handles serious incidents such as self-harm.
Commission head of investigations Nigel Ellis said: "Clearly, there are particularly challenging safety issues that have to be managed at mental health trusts.
"It is crucial that every trust monitors and manages risks in order to protect the safety of patients.
"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."
The commission visited the trust on 13 February following concerns raised by patients' relatives and the Mental Health Act Commission about how serious incidents were being investigated.
The investigation will examine whether the trust takes appropriate action to address the root causes of incidents in a way that would improve services and prevent similar events reoccurring.
It will focus on the period from April 2005 to the present and will involve interviews with people both from within and outside the trust.
The trust employs 3,800 staff across 32 sites and provides care for up to 18,000 patients at any one time.
In addition to serving residents of Ealing, Hounslow, Hammersmith and Fulham, it provides specialist and forensic mental health services.
The services at Broadmoor Hospital are not the main focus of the investigation.
A report is expected to be published in nine to 12 months' time.
A spokesman at the trust said the Healthcare Commission's decision was of serious concern but any guidance was welcome.
He said: "We aim to deliver first class care and we are constantly striving to improve all aspects of our services.
"As a large mental health trust providing the full range of mental health services, we recognise that serious incidents do occur on occasion. Obviously, our aim is to minimise these and to ensure we respond appropriately when things do go wrong.
"Our aim is to deliver the best possible services and we will work with the Healthcare Commission to ensure that happens."