Methodological differences between evaluations of medical home adoption might complicate readers' ability to draw conclusions across studies. To study whether associations between medical home adoption and patient care are affected by methodological choices. Among 71 practices participating in the Pennsylvania Chronic Care Initiative (a medical home pilot), we estimated cross-sectional and longitudinal associations between 4 definitions of "medical home adoption" [National Committee on Quality Assurance (NCQA) recognition in year 3, Medical Home Index scores at baseline and 3, and within-practice changes in Medical Home Index scores between baseline and year 3] and utilization and quality. Six utilization and 6 quality measures. In cross-sectional analyses at year 3, NCQA recognition was associated with higher rates of nephropathy monitoring (7.23 percentage points; confidence interval, 0.45-14.02), breast cancer screening (7.48; 2.11-12.86), and colorectal cancer screening (8.43; 2.44-14.42). In longitudinal analyses, NCQA recognition was associated with increases in hospitalization rates (2.75 per 1000 patient-months; 0.52-4.98). In baseline cross-sectional analyses, higher Medical Home Index scores were associated with fewer ambulatory care-sensitive hospitalizations (-0.61 per 1000 patient per month; -1.11 to -0.11), all-cause emergency department visits (-6.80; -12.28 to -1.32), and ambulatory care-sensitive emergency department visits (-5.60; 10.32 to -0.88). There were no statistically significant associations between any other measure of medical home adoption and quality or utilization. The findings of medical home evaluations are sensitive to methodological choices. Meta-analyses, narrative reviews, and other syntheses of medical home studies should consider subdividing their findings by analytic approach.