We analyze the impact of COVID-19 diagnoses on student grades, retention, and on-time graduation at a large public university. Even though COVID-19 rarely causes major health complications for a typical university student, diagnosis and quarantine may cause non-trivial disruptions to learning. Using event study analysis, we find that a COVID-19 diagnosis decreased a student's term grade point average (GPA) modestly by 0.08 points in the semester of diagnosis without significant effects afterward. The results were the most pronounced for male students, individuals with face-to-face instruction, and those with higher GPAs before the pandemic. We do not find a significant increase in the incidence of failing or withdrawing from a course due to diagnosis. In addition, we find no general evidence that the diagnoses delayed graduation or significantly altered first-year retention. However, the University experienced significant grade inflation during the pandemic, which exceeded the estimated effects of any COVID-19 diagnoses.