Although the exact incidence of pulmonary thromboembolism (PTE) in small animals is unknown, it is thought that PTE is a substantial, under-diagnosed complication. The difficulty in diagnosing PTE in small animals is confounded by its subtle symptomatic presentation and a lack of clinical suspicion, coexisting disease states, and lack of noninvasive tests that are sensitive and specific for the diagnosis of PTE. Although numerous laboratory markers of coagulation have been studied, only the D-dimer assay has shown clinical utility in detecting early embolism in humans. This paper examines the use of D-dimer assays and other clinical modalities in the diagnostic approach to thromboembolic disease in small animals.