I bought a fully cooked ham. It was frozen, and it's now thawed. How long should I put in the oven to warm it up?
Since it's already fully-cooked, you don't need to be all that precise with time or temperature. The most important thing is to avoid drying it out, so use a roasting pan and add a little water to the bottom (not more than 1 cm) and cover it while it's reheating.
It's best if you have a meat thermometer; toss it in at 300° F / 150° C (or up to 350° F / 175° C if you're in a hurry) and aim for a temperature of about 140° F / 60° C. If you don't have a thermometer, this about.com page suggests 16-20 minutes per pound; it also suggests heating to 135° F which is also fine. But if you're not going by a thermometer then you'd better make sure that it's completely thawed first, all the way to the interior, lest you end up with a semi-frozen dinner.
If you also plan to glaze it then apply the glaze after it's been heated and raise the temperature to 400° F (205° C) as the above link suggests.
Good instructions. It is easy to dry the ham out too much when you are heating it (precooked ham). I use a baking pan (with lid) AND wrap it in foil prior to putting it in the pan. A little water in the pan is a MUST. I usually go with 325 for about 18 minutes per pound. The combination of pan with lid plus foil seems like overkill but it insures a nice moist ham.