OBJECTIVES: While there is ample information on the activities needed to transform into a patient-centered medical home (PCMH), previous research lacks focus on cost as an obstacle to transformation. This is particularly important in small primary care practices (<10 full-time equivalent [FTE] providers), which serve a large number of outpatients. Therefore, the objective of this study was to estimate the cost of achieving and sustaining PCMH recognition for small primary care practices. METHODS: Using semi-structured interviews, we developed a cost collection tool and disseminated it to a self-selected cohort of 11 small primary care practices that had previously achieved PCMH recognition from the NCQA. We assessed the cost of transformation between 2008 and 2011 using the tool. The cost of transformation was divided into four categories: the cost of NCQA patient centered recognition activities, the application cost of obtaining recognition, the cost of changes to practice culture, and the cost of external collaborations. Costs were averaged and weighted by the number of FTE providers in each practice in order to make the results comparable across practices. RESULTS: Three practices completed the tool. The weighted average cost of PCMH transformation was $35,508 per FTE provider in the year before recognition was achieved, and $38,218 in the recognition year itself. The most costly patient-centered activity (weighted average) in the pre-transformation year was “providing self-care support” ($4,863/FTE provider), while “measuring and improving performance” ($9,503/FTE provider) was the most costly in the transformation year. CONCLUSIONS: The cost of recognition as a PCMH is a substantial but not insurmountable barrier to practice transformation. This information may be used by payers and policymakers to direct financial resources to primary care practices as they transform to the PCMH model. Indirect financial resources that assist in collecting cost data may also promote diffusion of the PCMH model.