The method of deep-vein phlebography here described has been applied in 251 extremities of 159 patients over a period of two and one-half years. The results have often been decisive in planning treatment because of the importance of distinguishing between incompetence and thrombosis of the deep veins. The films to be exposed must be 86 cm. long and 36 cm. wide in order to show the desired portions of both legs simultaneously. The contrast medium is injected into a dorsal vein of the foot, and three carefully timed roentgenograms are made. Preliminary tests for sensitivity are necessary, and patients must be told to expect pain in the injected feet; other complications have been few. Correct interpretation of the phlebograms obtained depends on the diagnostician's awareness of the pitfalls here described, particularly in the diagnosis of thrombi.