Objectives-Peripherally inserted central catheters (PICCs) are associated with an increased risk of venous thrombosis. This study had 2 objectives: to estimate the incidence of upper extremity venous thrombosis associated with PICCs in oncology patients and to evaluate the role of Doppler sonography in antithrombotic prophylaxis. Methods-We conducted a prospective study with each patient being followed for 6 weeks. From April 2014 to October 2014, we analyzed a series of 245 consecutive oncology patients undergoing chemotherapy via PICCs, for an overall number of 246 PICC placements. We assessed the role of Doppler sonography for initiation of antithrombotic prophylaxis. The study group encompassed 2 cohorts of patients: those who received regular weekly Doppler screening for thrombosis prophylaxis and those who did not. Results-Of 246 insertions, we observed 90 episodes of upper extremity venous thrombosis (36.59%); 62 of them were asymptomatic in the Doppler group, and 28 were symptomatic in the no-Doppler group. Patients in the Doppler group had a significantly lower rate of thrombosis (0%) than those in the no-Doppler group (23.53%; P <.01). Conclusions-Our prospective study suggests that the rate of PICC-related upper extremity venous thrombosis in oncology patients is high, and the occurrence of symptomatic thrombosis could be lowered with regular weekly Doppler screening after PICC insertions.