My post disappeared, so you may see this twice! Not knowing where you are located or what type Japanese Maple you have, my top three guesses are heat stress, too much sun and too little water.

I think those are good guesses.

Madeline, it was an extremely brutal year on any tree this year. The tree most likely will recover on its own, though I would recommend cutting out the dead limbs as they will not re-leaf. They will look grayish in color and be very brittle. I would wait until spring to determine how much damage has been wrought. It looks to be like it is a red lace leaf and they do not do very well in full hot sun exposure. If they want to move it, I recommend that they wait till all the leaves have ...»