Objective To test for correlation between the growth in adoption of ambulatory electronic health records (EHRs) in the United States during 2010–2013 and hospital admissions and readmissions for elderly Medicare beneficiaries with at least one of four common ambulatory care–sensitive conditions (ACSCs). Data Sources SK&A Information Services Survey of Physicians, American Hospital Association General Survey and Information Technology Supplement; and the Centers for Medicare & Medicaid Services Chronic Conditions Data Warehouse Geographic Variation Database for 2010 through 2013. Study Design Fixed effects model estimated the relationship between hospital referral region (HRR) level measures of physician EHR adoption and ACSC admissions and readmissions. Analyzed rates of admissions and 30‐day readmissions per beneficiary at the HRR level (restricting the denominator to beneficiaries in our sample), adjusted for differences across HRRs in Medicare beneficiary age, gender, and race. Calculated physician EHR adoption rates as the percentage of physicians in each HRR who report using EHR in ambulatory care settings. Principal Findings Each percentage point increase in market‐level EHR adoption by physicians is correlated with a statistically significant decline of 1.06 ACSC admissions per 10,000 beneficiaries over the study period, controlling for the overall time trend as well as market fixed effects and characteristics that changed over time. This finding implies 26,689 fewer ACSC admissions in our study population during 2010 to 2013 that were related to physician ambulatory EHR adoption. This represents 3.2 percent fewer ACSC admissions relative to the total number of such admissions in our study population in 2010. We found no evidence of a correlation between EHR use, by either physicians or hospitals, and hospital readmissions at either the market level or hospital level. Conclusions This study extends knowledge about EHRs' relationship with quality of care and utilization. The results suggest a significant association between EHR use in ambulatory care settings and ACSC admissions that is consistent with policy goals to improve the quality of ambulatory care for patients with chronic conditions. The null findings for readmissions support the need for improved interoperability between ambulatory care EHRs and hospital EHRs to realize improvements in readmissions.