The rate of corrosion of the reinforcing bars is one of the important parameters required to estimate the residual service-life of a reinforced concrete (RC) bridge deck. In the present study, first, the linear polarization resistance technique was used to measure the corrosion rates of plain mild steel and cold twisted deformed (CTD) bar specimens, which were typically used in the older existing bridges. To consider the variability of a corrosion rate, the frequency distributions of the corrosion rates for the two types of bars were determined. Next, a probabilistic approach was adopted for assessing an existing RC girder-and-slab road bridge deck, subjected to corrosion of bars attributable to air-borne chlorides. A computational model was developed using the Monte Carlo simulation method, to assess the reduction in the flexural capacity of a typical girder. It was observed that the reduction in the mean capacity and the dispersion of the capacity with respect to time, were high with the measured statistical parameters of the corrosion rate of CTD bars. © 2014 American Society of Civil Engineers.