Background: Tobacco quitlines offer clinicians a means to connect their patients with evidence-based treatments. Innovative methods are needed to increase clinician referral. Methods: This is a clinic randomized trial that compared usual care (n=25 clinics) vs a pay-for-performance program (intervention) offering $5000 for 50 quitline referrals (n=24 clinics). Pay-for-performance clinics also received monthly updates on their referral numbers. Patients were eligible for referral if they visited a participating clinic, were 18 years or older, currently smoked cigarettes, and intended to quit within the next 30 days. The primary outcome was the clinic's rate of quitline referral (ie, number of referrals vs number of smokers seen in clinic). Results: Pay-for-performance clinics referred 11.4% of smokers (95% confidence interval [CI], 8.0%-14.9%; total referrals,1483) compared with 4.2% (95% CI, 1.5%-6.9%; total referrals, 441) for usual care clinics (P=.001). Rates of referral were similar in intervention vs usual care clinics (n=9) with a history of being very engaged with quality improvement activities (14.1% vs 15.1%, respectively; P=.85). Rates were substantially higher in intervention vs usual care clinics with a history of being engaged (n=22 clinics; 10.1% vs 3.0%; P=.001) or less engaged (n=18 clinics; 10.1% vs 1.1%; P=.02) with quality improvement. The rate of patient contact after referral was 60.2% (95% CI, 49.7%-70.7%). Among those contacted, 49.4% (95% CI, 42.8%-55.9%) enrolled, representing 27.0% (95% CI, 21.3%-32.8%) of all referrals. The marginal cost per additional quitline enrollee was $300. Conclusion: A pay-for-performance program increases referral to tobacco quitline services, particularly among clinics with a history of less engagement in quality improvement activities.