Erhard Seminars Training (est) is a large-group experience that is becoming widely available in this country. This is the first case report in the professional literature of psychiatric disturbance following est training. Five patients, only one of whom had a history of psychiatric disturbance, developed psychotic symptoms including grandiosity, paranoia, uncontrollable mood swings, and delusions. Further work is necessary to ascertain the factors that determine outcome in est.