Shared psychotic disorders usually happen in people in long-term relationships in which the person who has the psychotic disorder is dominant and the other person is passive.
Shared psychotic disorders can also happen in groups of people who are closely involved with a person who has a psychotic disorder (called folie à plusiers, or "the madness of many"). For instance, this could happen in a cult if the leader is psychotic and his or her followers take on their delusions.