Background: Many patients with behavioral health concerns seek services for their problems from primary care providers (PCPs) rather than specialty mental health services. This study investigated whether referrals by PCPs to integrated behavioral health specialists could be predicted by PCPs’ stigmatizing attitudes towards mental illness, blaming of patients for their problems, and beliefs about the causes of mental illness. Method: Participants were all PCPs (N = 22) from three integrated primary care clinics, all part of the same Federally Qualified Health Center. PCPs completed a brief packet of questionnaires. Referral rates (percentage of unique patients seen in the prior 3 months who were referred to integrated behavioral health specialists) were extracted from electronic medical records. Results: PCPs showed moderate blame and low stigma towards patients with mental illness. PCPs reported believing mental illnesses were most strongly caused by environmental and biological factors, compared to psychological factors. Approximately 16% of patients seen by PCPs were referred to behavioral health specialists. Blame and stigma were not related to referral rates, but greater endorsement of biological causes was related to lower referral rates. Conclusions: Educating PCPs about the psychosocial determinants of behavioral health problems might increase willingness to refer patients to integrated care specialists.