Objective This article focuses on design, training, and delivery of motivational interview (MI) in a longitudinal randomized controlled trial intended to assess the efficacy of two separate interventions designed to increase colorectal screening when compared to a usual care, control group. One intervention was a single-session, telephone-based MI, created to increase colorectal cancer screening within primary care populations. The other was tailored health counseling. We present the rationale, design, and process discussions of the one-time motivational interviewing telephone intervention. We discuss in this paper the training and supervision of study interventionists, in order to enhance practice and research knowledge concerned with fidelity issues in motivational interview interventions. Methods To improve motivational interviewing proficiency and effectiveness, we developed a prescribed training program adapting MI to a telephone counseling session. Results The three interventionists trained in MI demonstrate some MI proficiency assessed by the motivational interviewing treatment integrity scale. In the post-intervention interview, 20.5% of the MI participants reported having had a CRC screening test, and another 19.75% (n = 16) had scheduled a screening test. Almost half of the participants (43%) indicated that the phone conversation helped them to overcome the reasons why they had not had a screening test. Conclusions Ongoing supervision and training (post-MI workshop) are crucial to supporting MI fidelity. The trajectory of learning MI demonstrated by the interventionists is consistent with the eight stages of learning MI. The MI road map created for the interventionists has shown to be more of a distraction than a facilitator in the delivery of the telephone intervention. MI can, however, be considered a useful tool for health education and warrants further study. Practice implications MI training should include consistent training and process evaluation. MI can, however, be considered a useful tool for health education and warrants further study. MI can also be adapted to diverse health promotion scenarios.