Transmission failure?

Appears to slip out of drive and into neutral when stopped briefly at a light. When I turned the ignition off, and re-started it, put it in drive it went into gear. And promptly slipped out of gear when I again stopped briefly. When I parked the vehicle, waited and started it again, the car went in to drive, but it will not go into any other gear. Likewise, when I turned off the ignition, waited, started it again, and put it in reverse, it went into reverse, but would not go into any other gear. This problem began without any warning. Could this problem indicate the need for a complete transmission overhaul?