Our data, along with the literature review we have undertaken, suggest that depression seen in the course of panic disorder most commonly represents symptomatic elaboration or complication of panic disorder. Less often it represents an associated independent entity or, more hypothetically, an alternative clinical expression of a shared underlying diathesis for both conditions. Future prospective research efforts, especially along familial-genetic lines, are needed to clarify the precise nature of the cross-sectional and longitudinal overlap of anxiety and depressive states.