Objectives: To determine the frequency of venous thromboembolism (VTE) in the adolescent and young adult oncology population and the effects of age and cancer type on VTE, and to characterize adolescent and young adult oncology admissions at US children's hospitals. Study design: We extracted data on oncology patients 15 to 24 years of age who were discharged from 35 hospitals in the Pediatric Hospital Information System (PHIS) between 2001 and 2008. Results: Of 9721 unique patients, VTE occurred in 511 (5.3%). An elevated OR of VTE occurred in patients 18 to 20 and 21 to 24 years of age (OR, 1.65; 95% CI, 1.36-2.00 and OR, 1.67; 95% CI, 1.21-2.32, respectively) compared with that in patients 15 to 17 years old. Patients with leukemia (OR, 5.53; 95% CI, 3.63-8.42) and bone/soft tissue sarcomas (OR, 4.32; 95% CI, 2.80-6.69) had a higher risk of VTE compared with patients with brain tumors. The number of adolescent and young adult oncology admissions to pediatric hospitals increased 31.9%, from 5409 admissions in 2001 to 7134 admissions in 2008. Conclusions: Adolescent and young adult oncology patients, a growing population at pediatric hospitals, experience VTE as a common complication. Pediatricians should implement adolescent and young adult-specific studies to develop a standardized approach to preventing this adverse event.