The predictive utility of proximity of primary care providers (PCPs) to mental health providers (MHPs) in referral rate and referral success was examined. Referrals from all PCPs in three New Jersey primary care clinics with primary care mental health integration (PC-MHI) to MHPs for fiscal year 2009 (October 1, 2008 through September 30, 2009) were included. Regression analyses supported the hypotheses that proximity significantly predicts both rate of referral per visit and rate of referral per unique patient. The hypothesis that proximity predicts referral success was not supported. Further research might seek to determine if additional variables moderate the relationship between provider proximity and referral rate. Implications of the findings for colocated programs were discussed.