Computer simulations are compared with measurements of the three-dimensional, unsteady scavenging flows of a motored, crankcase-scavenged, two-stroke engine. Laser Doppler velocimetry measurements were made on a modified Suzuki DT-85 ported engine. Calculations were performed using KIVA-3, a computer program that efficiently solves the transfer and exhaust port flows along with those in the cylinder. Measured and computed cylinder pressures and velocities are compared. Pressures agree well over the cycle as do the velocities at the transfer port/cylinder interface. In-cylinder velocities differ in detail, but the tumbling motion in the cylinder is well replicated in a vertical plane passing through the cylinder axis.