Background: The patient-centered medical home (PCMH) concept requires collaboration among clinicians both within the medical home clinic, and outside the clinic. As we redesign health information technology (HIT) to support transformation to the PCMH, we need to better understand these collaboration patterns. This study provides quantitative data describing these collaborations in order to facilitate the design of systems to allow for more efficient collaboration. Approach: Eighty-four clinicians in eight clinics identified their two most recent significant collaborators-one each within the clinic and in the medical neighborhood. They also identified the communication channels used in these collaborations. We used k-means clustering to identify communication patterns. Results: Within the clinic, half of the primary care providers (PCPs) identified a care manager as their most recent collaborator. Outside specialists were their most common external collaborators. Ninety-two percent of the non-PCP participants identified PCP's as their most recent internal collaborators. The best model for communication channel usage (p <.0001) had six clusters. In general, inside communications were more informal but outside collaborations were more often formal written communications (faxes, letters) or the exchange of electronic health record progress notes. But there were exceptions to these patterns and in many cases multiple channels were used for the same collaboration. Conclusion: Systems design (and redesign) needs to focus on reducing communications load and increasing communication effectiveness while maintaining flexibility.