Every year, millions of students who would have qualified for financial aid do not complete the Free Application for Federal Student Aid (FAFSA). Discouragingly, many of these students come from lower-income families and would have qualified for Pell Grants that do not have to be repaid. Using data from the Beginning Postsecondary Students Longitudinal Study (BPS:04/06) and logistic regression analysis, this study examined the relationship between filing a FAFSA and within-year persistence rates of first-year, fulltime college students. Results show that after controlling for background characteristics and college experience variables, students who filed a FAFSA have 72% higher odds of persisting than their peers who do not file. The effect of filing a FAFSA was even more significant among lower-income Pell Grant eligible students, as these FAFSA filers have 122% higher odds of persisting compared to their lower-income peers who did not file a FAFSA. These results emphasize the critical need for targeted public policies and institutional practices aimed at increasing FAFSA completion rates. (Contains 3 tables and 1 footnote.)