Purpose:  To assess the impact on health care cost and quality among seniors of a patient-centered medical home (PCMH) pilot at Group Health Cooperative, an integrated health care system in Washington State.  Design and Methods:  A prospective before-and-after evaluation of the experience of seniors receiving primary care services at 1 pilot clinic compared with seniors enrolled at the remaining 19 primary care clinics owned and operated by Group Health. Analyses of secondary data on quality and cost were conducted for 1,947 seniors in the PCMH clinic and 39,396 seniors in the 19 control clinics. Patient experience with care was based on survey data collected from 487 seniors in the PCMH clinic and of 668 in 2 specific control clinics that were selected for their similarities in organization and patient composition to the pilot clinic. Results:  After adjusting for baseline, seniors in the PCMH clinic reported higher ratings than controls on 3 of 7 patient experience scales. Seniors in the PCMH clinic had significantly greater quality outcomes over time, but this difference was not significant relative to control. PCMH patients used more e-mail, phone, and specialist visits but fewer emergency services and inpatient admissions for ambulatory care sensitive conditions. At 1 and 2 years, the PCMH and control clinics did not differ significantly in overall costs.  Implications:  A PCMH redesign can be associated with improvements in patient experience and quality without increasing overall cost.