Objective: To present a case report of folie simultanee in monozygotic
twins. The literature describing folie a deux in twins is also review
ed and the common clinical findings are presented. Method: Case presen
tation and review of the literature. Results: Clinical observations of
monozygotic twins with folie simultanee suggest that the delusions fe
nd to progress over time with each twin reinforcing the delusion in th
e second. Conclusions: The concept of a delusion resonating between in
dividuals may account for the rapid progression and escalation of thes
e delusions.