The flow produced by a synthetic jet actuator located in one wall of a microchannel is investigated using computational l1uid dynamics (CFD) simulations. In the case of no cross-flow, the ejected vortices travel to the opposite wall and replenish the remains of the vortex left behind from the previous cycle. When cross-flow is added, the vortex penetration increases with both stroke length and frequency. The flow in the cavity appears to be nearly symmetrical. with the greatest effect seen near the orifice. In the orifice itself, three-dimensional effects are more noticeable with decreasing jet-to-cross-flow momentum ratio. The microchannel cross-flow causes the vortices to tumble about their transverse axis, the effect of which also increases with decreasing jet-to-cross-flow momentum ratio.