Deep vein thrombosis (DVT) of the lower extremity is a multifactorial and potentially fatal complication following stroke. However, repetitive impact on the lower extremity is a relatively uncommon risk factor for DVT. We report an ambulatory hemiparetic stroke patient who, without classic DVT risk factors, developed a lower extremity DVT probably due to repetitive impact on the popliteal fossa after the inappropriate use of a seated leg flexion machine. This case can remind physiatrists and therapists of the importance of preventing patients from using non-ergonomic postures during training sessions.