Despite decades of interest in Ph.D. student outcomes, there have been few comprehensive studies of doctoral student completion. Compared to research on undergraduate students, longitudinal studies of doctoral student completion in multiple disciplines at multiple institutions are exceptionally rare. As a consequence, there is relatively scant evidence to support general assertions regarding estimates and the temporal dimensions of completion rates. This study estimated and compared completion rates over time for 5,323 Ph.D. students from five fields in 16 institutions by field, gender, ethnicity, and prior Master's degree at entry status using the longitudinal database of the AAU/AGS Project for Research on Doctoral Education. Comparisons of the results with conventional wisdom and prior studies are offered. The findings can potentially inform the development of interventions and policy directed toward achieving desirable completion rates. (Contains 5 figures and 1 table.)