Overview of study design. The objectives of this study were to: (1) identify factors that influenced adult fellows to choose careers in hematology and oncology; (2) define the timing during the course of medical and graduate education when trainees decide to pursue careers in hematology and oncology; and (3) identify trends in preferences and plans for practice after fellowship. Data were obtained from 3 sources: (1) ASH In-Service Exam surveys, administered annually to all adult hematology and hematology/oncology fellows in the United States from 2010 to 2016, with a total of 8789 participants during the study period; (2) interviews with graduating and recently graduated adult hematology/oncology fellows at a single hematology/oncology fellowship program in the northeastern United States (n = 8); and (3) 3 focus groups held at the ASH annual meeting in December 2016, involving program directors (n = 12), adult hematology/oncology fellows (n = 12), and practicing adult hematology/oncology clinicians (n = 10) from a mix of academic centers and community programs in 21 states.