Previous research on birth order has consistently shown that later-borns have lower educational attainment than first-borns; however, it is not known whether there are birth order patterns in college major. Given evidence that parents disproportionately invest in first-born children, there are likely to be birth order patterns attributable to differences in both opportunities and preferences, related to ability, human capital specialization through parent-child transfers of knowledge, and personality. Birth order patterns in college major specialization may shed light on these explanatory mechanisms and may also account for long-term birth order differences in educational and labour market outcomes. Using Swedish population register data and sibling fixed effects, we find large birth order differences in university applications. First-borns are more likely to apply to, and graduate from, medicine and engineering programs at university, while later-borns are more likely to study journalism and business programs, and to attend art school. We also find that these birth order patterns are stronger in high-socioeconomic status families and that differences in college major explain approximately half of the within-family birth order differences in long-term earnings. These results indicate that early life experiences and parental investment shape sibling differences in ability, preferences, and ambitions even within the shared environment of the family.