The patient presenting to the emergency department (ED) with a painful swollen lower extremity is considered to have deep venous thrombosis (DVT) until this diagnosis can be ruled out. This clinical presentation, however, is far from specific and the differential diagnosis includes symptomatic Baker's cyst, also known as pseudothrombophlebitis syndrome (PTP). This article presents two cases of PTP and reviews the literature relevant to diagnosis of DVT and PTP. Ultrasonography is now the diagnostic test of choice for both DVT and PTP, being safe, accurate, noninvasive, and rapid, and should ideally be available for use in the ED.