At an agreed time, each of them told the duty psychiatrist that they were hearing a voice in their head that said the words "empty," "hollow," and "thud." That was the only lie they would be allowed to tell. Otherwise they had to behave completely normally.
All eight were immediately diagnosed as insane and admitted into the hospitals. Seven were told they had schizophrenia; one manic depression.
Rosenhan had expected the experiment would last a couple of days. That's what he'd told his family: that hey shouldn't worry and he'd see them in a couple of days. The hospital didn't let him out for two months.
In fact, they refused to let any of the eight out, for an average of nineteen days each, even though they all acted completely normally from the moment they were admitted.
There was only one way out. They had to agree with the psychiatrist that they were insane and then pretend to get better.
One mental hospital challenged Rosenhan to send some more fakes, guaranteeing they'd spot them this time. Rosenhan agreed, and after a month, the hospital proudly announced they had discovered forty-one fakes. Rosenhan then revealed he'd sent no one to the hospital.