The first part involved the use of healthy associates or “pseudopatients” (three women and five men, including Rosenhan himself) who briefly feigned auditory hallucinations in an attempt to gain admission to 12 different psychiatric hospitals in five different states in various locations in the United States. All were admitted and diagnosed with psychiatric disorders. After admission, the pseudopatients acted normally and told staff that they felt fine and had no longer experienced any additional hallucinations. All were forced to admit to having a mental illness and agree to take antipsychotic drugs as a condition of their release. The average time that the patients spent in the hospital was 19 days. All but one were diagnosed with schizophrenia “in remission” before their release.
*The second part of his study involved an offended hospital administration challenging Rosenhan to send pseudopatients to its facility, whom its staff would then detect. Rosenhan agreed and in the following weeks out of 193 new patients the staff identified 41 as potential pseudopatients, with 19 of these receiving suspicion from at least one psychiatrist and one other staff member. *In fact, Rosenhan had sent no pseudopatients to the hospital.
The study concluded “it is clear that we cannot distinguish the sane from the insane in psychiatric hospitals” and also illustrated the dangers of dehumanization and labeling in psychiatric institutions.

• none of the pseudopatients were identified as impostors by the hospital staff, although many of the other psychiatric patients seemed to be able to correctly identify them as impostors.*
• Hospital notes indicated that staff interpreted much of the pseudopatients' behavior in terms of mental illness. […] The patients' normal biographies were recast in hospital records along the lines of what was expected of schizophrenics by the then-dominant theories of its etiology.*
• “If I were to drink a quart of blood and, concealing what I had done, come to the emergency room of any hospital vomiting blood, the behavior of the staff would be quite predictable. If they labeled and treated me as having a bleeding peptic ulcer, I doubt that I could argue convincingly that medical science does not know how to diagnose that condition."*