If I am an incorporated physician, do I need two National Provider Identifiers (NPIs)?

Yes. If you have a practice association (PA) or a limited liability corporation (LLC), and it holds any contracts with payers, or if payment is ever made to the PA or LLC, or in the name of the PA or LLC, then it needs to acquire a Type 2 NPI in addition to your individual Type 1 NPI.

Even if the practice association is an S corporation or a "disregarded entity" (i.e., tax return can be filed in the physician's name), the above applies. From an NPI perspective, an S corporation is no different from a limited liability corporation or any other type of corporation; if the PA receives payments, it must have its own Type 2 NPI.