To document the temporal trends in alternative primary care models in which physicians, nurse practitioners (NPs), or physician assistants (PAs) engaged in care provision to the elderly, and examine the role of these models in serving elders with multiple chronic conditions and those residing in rural and health professional shortage areas (HPSAs). Serial cross-sectional analysis of Medicare claims data for years 2008, 2011, and 2014. Primary care outpatient setting. Medicare fee-for-service beneficiaries who had at least 1 primary care office visit in each study year. The sample size is 2 471 498. Physician model-Medicare beneficiary's primary care office visits in a year were conducted exclusively by physicians; shared care model-conducted by a group of professionals that included physicians and either NPs or PAs or both; NP/PA model: conducted either by NPs or PAs or both. There was a decrease in the physician model (85.5% to 70.9%) and an increase in the shared care model (11.9% to 23.3%) and NP/PA model (2.7% to 5.9%) from 2008 to 2014. Compared with the physician model, the adjusted odds ratio (AOR) of receiving NP/PA care was 3.97 (95% CI 3.80-4.14) in rural and 1.26 (95% CI 1.23-1.29) in HPSAs; and the AOR of receiving shared care was 1.66 (95% CI 1.61-1.72) and 1.14 (95% CI 1.13-1.15), respectively. Beneficiaries with 3 or more chronic conditions were most likely to received shared care (AOR = 1.67, 95% CI 1.65-1.70). The increase in shared care practice signifies a shift toward bolstering capacity of the primary care delivery system to serve elderly populations with growing chronic disease burden and to improve access to care in rural and HPSAs.