Concurrent pleural and pericardial effusions are not an unusual finding, but their differential diagnosis remains uncertain. Medline-based review identified an extensive list of infectious, inflammatory, neoplastic, iatrogenic, and myriad other etiologies. A single retrospective study had addressed this presentation. Several principles of a diagnostic workup are suggested, acknowledging that a significant minority of patients may not require a comprehensive workup and remain ‘idiopathic’.