Most studies on adolescent screening, brief intervention, and referral to treatment (SBIRT) have examined substance use outcomes. However, it may also impact service use and comorbidity-an understudied topic. We address this gap by examining effects of SBIRT on health care use and comorbidities. In a randomized trial sample, we assessed 3 SBIRT care modalities: (1) pediatrician-delivered, (2) behavioral clinician-delivered, and (3) usual. Medical comorbidity and health care use were compared between a brief-intervention group with access to SBIRT for behavioral health (combined pediatrician and behavioral clinician arms) and a group without (usual care) over 1 and 3 years. Among a sample of eligible adolescents (n = 1871), the SBIRT group had fewer psychiatry visits at 1 year (incidence rate ratio [iRR] = 0.76; P = .05) and 3 years (iRR = 0.65; P < .05). Total outpatient visits did not differ in year 1. The SBIRT group was less likely to have mental health diagnoses (odds ratio [OR] = 0.69; 95% confidence interval [CI] = 0.48-1.01) or chronic conditions (OR = 0.66; 95% CI = 0.45-0.98) at 1 year compared with those in usual care. At 3 years, the SBIRT group had fewer total outpatient visits (iRR = 0.85; P < .05) and was less likely to have substance use diagnoses (OR = 0.64; 95% CI = 0.45-0.91) and more likely to have substance use treatment visits (iRR = 2.04; P < .01). Providing SBIRT in pediatric primary care may improve health care use and health, mental health, and substance use outcomes. We recommend further exploring the effects of SBIRT on these outcomes.