A sizeable body of research has demonstrated that expressed emotion (EE) pr
edicts clinical relapse in a number of distinct psychiatric disorders. Thes
e findings have provided the impetus for the development of interventions t
hat attempt to reduce patients' relapse rates by modifying aspects of the f
amily environment believed to be associated with high levels of EE. Despite
the efficacy of these treatments, however, we know little about how EE dev
elops in relatives of psychiatric patients or about the mechanisms through
which high EE leads to relapse. Moreover, there is not a coherent theory th
at attempts to integrate findings concerning the impact of high EE on relap
se in different disorders. The purpose of this article is to elucidate a di
athesis-stress conceptualization of EE to explain both the development and
manifestation of high EE in relatives of disordered patients and the impact
of high EE on the course of patients' disorders. In this context, we use a
diathesis-stress perspective to examine why EE predicts symptom relapse an
d poor clinical outcome in schizophrenia, depressive disorders, and borderl
ine personality disorder. We conclude by discussing treatment implications
of the diathesis-stress perspective and by outlining what we believe are fr
uitful directions for future research.