PURPOSE: Persistent workforce shortages exist in some radiology subspecialties. Residents' motivations for selecting particular fellowships, as well as their perceptions of the subspecialty fields, heavily influence the supply of new radiologists to these areas. The authors investigated the factors residents consider most important in subspecialty choice, fellowship choice patterns between 1999 and 2008, and changes that might attract residents to one particular shortage field: pediatric radiology. MATERIALS AND METHODS: An online questionnaire was developed and sent to 1,000 radiology trainees in the United States using contact information from the ACR's national resident database. Anonymized responses were evaluated using analysis of variance and logistic regression models. RESULTS: Leading factors for fellowship selection were "area of strong personal interest," "advanced/multimodality imaging," and "intellectual challenge." Compensation ranked low, 13th among 20 factors. Large shifts in subspecialty preference were seen between 1999 and 2008. Those with a pediatric radiology preference ranked "physician-physician interaction," "physician-patient contact," and "altruism" higher than respondents selecting other subspecialties. Respondents believed that pediatric radiologists make less money than other subspecialists ($325,000 vs $385,000 per year). There was no association between choosing pediatric radiology and gender, age, research plans, or parental status. CONCLUSIONS: Multiple factors account for subspecialty selection among residents, and it is useful to understand these factors when attempting to recruit residents to specific subspecialties. To ease the workforce shortage in pediatric radiology, advanced and varied imaging modalities, numerous job opportunities, and well-paid private practice positions should be emphasized to residents.