Objective: To investigate the effects of two monetary incentives on response rates to postal questionnaires from primary care physicians (PCPs).Study Design and Setting: The PCPs were randomized into three arms (n = 550 per arm), namely (1) (sic)5 sent with the questionnaire (cash); (2) entry into a draw on return of completed questionnaire (prize); or (3) no incentive. Effects of incentives on response rates and item nonresponse were examined, as was cost-effectiveness.Results: Response rates were significantly higher in the cash (66.1%; 95% confidence interval [CI]: 61.9, 70.4%) and prize arms (44.8%; 95% CI: 40.1,49.3%) compared with the no-incentive arm (39.9%; 95% CI: 35.4, 44.3%). Adjusted relative risk of response was 1.17 (95% CI: 1.02, 1.35) and 1.68 (95% CI: 1.48, 1.91) in the prize and cash arms, respectively, compared with the no-incentive group. Costs per completed questionnaire were (sic)9.85, (sic)11.15, and (sic)6.31 for the cash, prize, and no-incentive arms, respectively. Compared with the no-incentive arm, costs per additional questionnaire returned in the cash and prize arms were (sic)14.72 and (sic)37.20, respectively.Conclusion: Both a modest cash incentive and entry into a prize draw were effective in increasing response rates. The cash incentive was most effective and the most cost-effective. Where it is important to maximize response, a modest cash incentive may be cost-effective. (C) 2014 Elsevier Inc. All rights reserved.