**Short answer: usually not for commercial payers, sometimes for Medicare.** - Medicare allows limited 'incident-to' billing under the supervising physician for established patients and established problems, with the physician on site. - Most commercial payers and Medicaid MCOs require the rendering provider to be enrolled; billing under another NPI is misrepresentation. The safe path is to hold the claims and submit once the NP's effective date is issued, watching the timely-filing limits.