The purpose of this study is to examine referrals of nurse practitioners providing primary healthcare (PHC NPs) to better understand how PHC NPs collaborate with other healthcare professionals and contribute to interprofessional care. The analysis is based on the data from a survey of 378 PHC NPs registered in Ontario, Canada in 2008. Overall, 69% of PHC NPs made referrals to family physicians (FPs) and 67% of PHC NPs received referrals from FPs. Almost 50% of PHC NPs had bidirectional referrals between them and FPs. Eighty-nine percent of PHC NPs made referrals to specialist physicians. Bidirectional referrals between PHC NPs and social workers and mental health workers were common in family health teams and community health centers. Patterns of referrals (bidirectional, unidirectional and no referrals) between PHC NPs and FPs, social workers, mental and allied health workers in various practice settings indicate development of collaborative relationships between PHC NPs and other healthcare professionals and reflect the influence of practice models on delivery of interprofessional care. These findings are discussed in light of the development of NPs' role and integration of PHC NPs in the Ontario healthcare system. Implications for policy changes and future research are also suggested.