Background: Acquiring proficiency in motivational interviewing (MI) may be more difficult than generally believed, and training research suggests that the standard one-time workshop format may be insufficient. Although nurses represent one of the professions that have received most training in MI, training in this group has rarely been systematically evaluated using objective behavioral measures. Aims: To evaluate an enhanced MI training program, comprising a 3.5-day workshop, systematic feedback on MI performance, and four sessions of supervision on practice samples. Methods: Nurses (n = 36) in Swedish child health services were trained in MI. Skillfulness in MI was assessed using the Motivational Interviewing Treatment Integrity (MITI) Code. Effects of training were compared to beginning proficiency thresholds. Results: Participants did not reach beginning proficiency thresholds on any of the indicators of proficiency and effect sizes were small. Conclusions: The present study adds to a growing body of literature suggesting that the current standard MI training format may not provide practitioners with enough skillfulness. Moreover, the results indicate that even enhanced training, including systematic feedback and supervision, may not be sufficient. Suggestions for improved MI training are made.