*† ‡ Many maritime applications involve the use of dynamically moving hydrofoils. Numerical simulations using Reynolds averaged Navier-Stokes equations are carried out to analyze the effect of cavitation on the dynamic stall of an oscillating hydrofoil. It was found that the flow physics changes considerably with cavitation. The dynamic stall vortex (DSV) was formed at an angle of attack much smaller than for the non-cavitating case. The vortical structures were found to be distorted as compared to the non-cavitating case. Cavitation prevented the pairing process for the secondary vortices, and resulted in increased strength of tertiary and quaternary vortices, leading to large oscillation in the coefficient of lift during the downward pitching motion.