Background: The communication of relevant patient information between general practitioners (GPS) and medical specialists is important in order to avoid fragmentation of care thus achieving a higher quality of care and ensuring physicians' and patients' satisfaction. However, this communication is often not carried out properly. The objective of this study is to assess whether communication between GPS and medical specialists in the referral process is associated with the organisation of primary care within a country, the characteristics of the GPS, and the characteristics of the primary care practices themselves. Methods: An analysis of a cross-sectional survey among GPS in 34 countries was conducted. The odds ratios of the features that were expected to relate to higher rates of referral letters sent and communications fed back to GPS were calculated using ordered logistic multilevel models. Results: A total of 7183 GPS from 34 countries were surveyed. Variations between countries in referral letters sent and feedback communication received did occur. Little of the variance between countries could be explained. GPS stated that they send more referral letters, and receive more feedback communications from medical specialists, in countries where they act as gatekeepers, and when, in general, they interact more with specialists. GPS reported higher use of referral letters when they had a secretary and/or a nurse in their practice, used health information technologies, and had greater job satisfaction. Conclusions: There are large differences in communication between GPS and medical specialists. These differences can partly be explained by characteristics of the country, the GP and the primary care practice. Further studies should also take the organisation of secondary care into account.