Question
my begonias are dropping their leaves.  what might be the problem?  the leaves are nice healthy ones.

Answer
Hi Sue
Double check for any pests; mealy bugs (white cottonish looking bugs under the leaves), white fly (actually small white flies around the plant) or spidermite (check for small webs in between the leaf brackets).
If this is fine, make sure you are not overwatering.  Check to make sure the soil is dry at least 1" down before watering.  Also, do not allow the pot to sit in water as this could cause root rot.
Hope this has helped you, Sue.
Leslie