To determine the natural history of calf deep venous thrombosis (C-DVT), an analytic review of the 20 relevant English-language papers published since 1942 was performed. Remarkably little methodologically sound research on this subject was found. However, available evidence suggests that C-DVT propagates to the thigh in up to 20% of cases and that propagation invariably occurs before embolization. No fatal emboli were reported in patients presenting with isolated C-DVT. Traditional anticoagulation treatment with heparin sodium and warfarin sodium of symptomatic patients with C-DVT appears to prevent extension, embolization, and early recurrence. There is no convincing evidence that C-DVT leads to chronic venous insufficiency or whether the risks of anticoagulation exceed the risks of no treatment. As an option to anticoagulation, physicians may choose to follow patients with C-DVT with serial impedance plethysmography, treating only if there is evidence of proximal extension.