Deep-vein thrombosis of the lower limb is common, yet the importance of isolated calf deep-vein thrombosis is poorly understood and the treatment is controversial. This retrospective study documented that 13% of fatal pulmonary emboli originated only from calf deep-vein thrombosis. This rate is similar to that in another study (15%), suggesting that isolated calf deep-vein thromboses do produce fatal pulmonary emboli.