Cancer in adolescents and young adults has unique features in addition to the special medical, physical, psychological, and social needs of patients in this age group. The spectrum of malignant diseases is different from that in any other period in life, and it is strikingly different from the pattern in older persons. More people 15–25 years of age are diagnosed to have cancer than during the first 15 years of life. During the last 25 years, the incidence of cancer in this age range has increased faster while the increase in their cancer survival rates has been significantly lower than in younger or older patients, especially in comparison to results of the national pediatric cooperative cancer groups. Thus the 5-year outcome in 15–19 year olds with leukemias and sarcomas is not only worse than in younger patients, but also lower in this population at large than in patients of the same age treated at Children's Cancer Group institutions. In the United States, only ∼5% of 15–25 year olds with cancer are entered onto clinical trials, in contrast to 60–65% of younger patients. Thus, cancer during adolescence and early adult life is an underestimated challenge that merits specific resources, solutions, and an international focus. Med Pediatr Oncol 2002;38:1–10. © 2002 Wiley-Liss, Inc.