We find that private-securitized loans perform worse than observably similar, nonsecuritized loans, which provides evidence for adverse selection. The effect of securitization is strongest for prime mortgages, which have not been studied widely in the previous literature and, in particular, prime adjustable-rate mortgages (ARMs): These become delinquent at a 30 % higher rate when privately securitized. By contrast, our baseline estimates for subprime mortgages show that private-securitized loans default at lower rates. We demonstrate, however, that “early defaulting loans” account for this: those that were so risky that they defaulted before they could be securitized.