To determine availability of and test whether on-site mental health providers (MHP) is associated with greater odds of reported mental health consultation and referral among primary care pediatricians.Pediatricians were identified from the American Medical Association's 2004 physician directory and stratified by region. Six hundred were randomly selected to receive a mail survey. The main independent variable was on-site MHP. The dependent variable was reported frequency (4-point rating) of mental health consultation and referral. Estimates were weighted to account for survey design and nonresponse.Overall response rate was 51%. The majority of respondents were male (56%), age ≥46 years old (59%), white (68%), and practicing in suburban locations (52%). Approximately half reported consultation with (44%) or referral to (51%) MHP always or often, but a few (17%) reported on-site MHP. After adjustment for demographic and practice characteristics, pediatricians with on-site MHP were more likely to consult (odds ratio [OR] 6.58, 95% confidence interval [95% CI] 3.55- 12.18) or refer (OR 4.25, 95% CI 2.19–8.22) than those without on-site MHP. Among those without on-site MHP, pediatricians with greater practice burden were less likely to consult (OR 0.69, 95% CI 0.48–0.99) or refer (OR 0.75, 95% CI 0.54–1.04) than those with lesser burden.Most pediatricians in the United States experienced practice-related burdens that limit mental health collaboration, but those with co-located services reported a greater likelihood of consultation and referral. Policy changes that encourage co-location of mental health services and limit practice burden may facilitate mental health consultation and referral.