Choosing a medical specialty is an important, complex, and not fully understood process. The present study investigated the factors that are related to choosing and rejecting medical specialties in a group of students and recent medical doctors. METHODOLOGY AND FINDINGS: A cross-sectional survey of 1,223 medical students and doctors was performed in Brazil in 2012. A standardized literature-based questionnaire was applied that gathered preferable or rejected specialties, and asked questions about extracurricular experiences and the influence of 14 factors on a Likert-type scale from 0 to 4. Specialties were grouped according to lifestyle categories: controllable and uncontrollable, which were subdivided into primary care, internal medicine, and surgical specialties. Notably, the time period of rejection was usually earlier than the time period of intended choice (p < 0.0001, χ(2) = 107.2). The choice mainly occurred during the internship period in medical school (n = 466; 38.7%). An overall large frequency of participation in extracurricular activities was observed (n = 1,184; 95.8%), which were highly associated with the respective medical area. Orthopedic surgery had the highest correlation with participation in specialty-specific organized groups (OR = 59.9, 95% CI = 21.6-166.3) and psychiatry was correlated with participation in research groups (OR = 18.0, 95% CI = 9.0-36.2). With regard to influential factors in controllable lifestyle specialties, "financial reason" (mean score ± standard deviation: 2.8 ± 1.0; median = 3) and "personal time" (3.1 ± 1.3; median = 4) were important factors. In primary care, these factors were less important (1.7 ± 1.3 and 1.7 ± 1.5, respectively; median = 2 for both), and higher scores were observed for "curricular internship" (3.2 ± 1.1, median = 4) and "social commitment" (2.6 ± 1.3, median = 3). CONCLUSION: The present findings provide important insights into developing strategies to stimulate interest in specialties based on the needs of the Brazilian healthcare system.