BACKGROUND: Clinician perceptions of a newly implemented electronic health record play an important role in its success or failure. OBJECTIVE: To measure changes in primary care clinician attitudes toward an electronic health record during the first year following implementation. DESIGN: Longitudinal survey. PARTICIPANTS: 86 primary care clinicians surveyed between December 2006 and January 2008. MEASUREMENTS: Perceived impact on overall quality of care, patient safety, communication, and efficiency at 1, 3, 6, and 12 months following implementation. RESULTS: Response rates for months 1, 3, 6, and 12 were 92%, 95%, 90%, and 82%, respectively. The proportion of clinicians agreeing that the EHR improved the overall quality of care (63% to 86%; p < 0.001), reduced medication-related errors (72% to 81%; p = 0.03), improved follow-up of test results (62% to 87%; p < 0.001), and improved communication among clinicians (72% to 93%; p < 0.001) increased from month 1 to month 12. During the same time period, a decreasing proportion of clinicians agreed that the EHR reduced the quality of patient interactions (49% to 33%; p = 0.001), resulted in longer patient visits (68% to 51%; p = 0.001), and increased time spent on medical documentation (78% to 68%; p = 0.006). Significant improvements in perceptions related to test result follow-up were first detected at 6 months, while those related to overall quality, efficiency, and communication were first identified at 12 months. CONCLUSIONS: Primary care clinicians report increasingly positive perceptions of a new electronic health record within 1 year of implementation across a spectrum of domains of care.