Background: Cancer among adolescents presents unique issues regarding diagnosis, treatment, late effects, and survival; but little is known about their healthcare costs, which are useful for economic evaluations and planning care. This study estimates total and cancer-attributable (net) medical costs for a population-based adolescent cancer cohort in British Columbia, Canada, by phase of care. Methods: Patients diagnosed with cancer aged 15 to 19 years from 1995 to 2009 were identified from the British Columbia Cancer Registry, and followed to December 31^st2010. Data were linked with clinical and provincial administrative healthcare databases covering all medically-necessary costs. Total resource-specific costs (Canadian $ 2012) by phase of care were estimated for all patients and specific common cancers. Net costs were calculated by subtracting healthcare costs for propensity-score-matched provincial samples of adolescents without cancer from cancer patient costs. Results: Of the 750 cases, approximately 26% had lymphoma, 17% germ cell, 14% bone and soft tissue sarcomas, 12% central nervous system (CNS), and 11% leukemia; 94% survived > = 1 year. Total mean pre-diagnosis costs per patient were $3657, of which $3554 was attributable to the cancer. First-year mean costs were $60,531 ($59,826). Continuing phase mean costs were $8,413 ($7,708). Final year of life mean costs were $224,243 ($221,018). Cancer types with highest costs were CNS (pre-diagnosis), leukemia (first-year); bone and soft tissue (continuing), and leukemia (end-of-life). Virtually all inpatient hospitalizations were cancer-related, representing ~40% of pre-diagnosis, ~62% of first-year, ~56%of continuing, and ~72%of end-of-life costs respectively. Conclusions: Management of adolescent cancer is costly, but is lower than for childhood cancer in all phases of care. Total costs, cancer-attributable costs, and inpatient activity were highest in the end-of-life period. Hospitalizations were the largest driver of costs in all post-diagnosis phases of care. Costs in the continuing phase, including surveillance and care for late effects, were 14% of first-year phase costs.