The gender composition of physician specialties varies dramatically with some becoming increasingly female predominant while others remain overwhelmingly male. In their analysis of physician workforce data, the authors demonstrate that despite large increases in the number of female physicians over 4 decades, the degree of gender segregation between specialties has not declined. The authors describe lessons from the highly gender-segregated U.S. workforce as a whole to understand these demographic patterns in the physician workforce. Echoing U.S. workforce findings, women physicians are becoming overrepresented in certain specialties, and this appears to be associated with a relative decline in earnings for physicians in these specialties over time. The authors found a strong negative relationship between the proportion of female physicians in a specialty and its mean salary, with gender composition explaining 64% of the variation in salaries among the medical specialties.Female physicians face biases in the workplace and fall behind male peers in leadership attainment, academic advancement, and earnings. Tenacious gender stereotypes and the conflation of gender and status contribute to these biases and reinforce occupational gender segregation. The clustering of women in certain specialties means these specialties will be disproportionately affected by gender bias. Recognizing the consequences of gender demographics within physician specialties is important to maintain the strong and diverse physician workforce needed to support the health care needs of the populations who depend on these specialties for care.