The Mental Health Act 1983 is an act of legislation passed by the U.K. Parliament. It is applicable to the people of Wales and England. Among the people receiving treatment in psychiatric indoor facilities, majority are those who get admitted voluntarily and they share the same rights with those who are admitted for any other physical disorder.These are informal patients. There is another group of patients among psychiatric population which need hospital admission on an involuntary basis for the sake of their own treatment and safety of themselves and the society. These are generally the very aggressive,  severely psychotic and suicidal subjects. These are called formal patients.

The Mental Health Act 1983 deals with  safeguarding  the rights of these formal patients who cannot take their own decision and thus protect them from any harm caused to them by their illness. It deals with the assessment as well as treatment of this group of patients. It provides a framework and guideline under which these patients may be compulsorily detained in a psychiatric facility or police custody and provided with necessary treatment with or without their consent.

The act is divided into 10 different parts. Some of which include topics like managing of the property and other affairs like marital issues of these patients. It also addresses issues about their criminal responsibilities, whether they are guilty by law or was their action completely a part of their illness. As the patient improves with treatment, it also has a provision for their discharge and continue with their treatment in the community and plan regular follow up visits.

However over the period of time, there were several drawbacks and flaws detected in the Mental Health Act 1983 and so certain changes have been made to this act and implemented in the Mental Health Act 2007 which is now available.