Electrochemical current and potential transients were measured during anodic oxidation of aluminum, on time scales of 0.1-100 ms after anodizing began. Aluminum foil samples were prepared by surface treatments yielding oxide films of thickness 5 nm or smaller. A mathematical model was developed for the transients based on steady-state and transient conduction phenomena established for much thicker anodic films. Model calculations and experimental transients were in quantitative agreement, indicating that the electrochemical behavior of the nanometer-thick films during their growth is strongly similar to that of anodic films. No electrochemical processes other than uniform oxide growth were detected, as might have been associated with defects constituting easy conduction paths. The rate of oxide growth was shown to be controlled by oxygen ion transfer at the film-solution interface.