Objectives Expenditure on research has grown substantially; however, a major challenge for conducting successful clinical research is the efficient recruitment of participants. We investigated factors influencing the rate at which general practitioners (GPs) recruit participants to a randomized controlled trial. Study Design and Setting We used data on 363 GPs recruiting participants for a randomized controlled trial of low back pain. Multivariate negative binomial regression was used to determine associations of characteristics of the GP and study operational aspects with the recruitment rate. Results GPs recruited 1,195 participants at a rate of 0.013 participants/day. GPs located in a high socioeconomic area recruited at half the rate as those located in a low socioeconomic area [incident rate ratio (IRR), 0.52; 95% confidence interval (CI): 0.37, 0.74]. A follow-up within 2 weeks of training the GP and a higher number of face-to-face visits were operational procedures associated with a higher rate of recruitment (IRR, 2.15; 95% CI: 1.58, 2.94 and IRR, 1.17; 95% CI: 1.11, 1.24, respectively). Other contacts made with a GP were not associated with recruitment. Conclusion The results suggested that the type of operational procedures used in clinical trial recruitment strategies are important aspects to consider. The ability to predict which GPs will recruit based on GP characteristics seems limited.