Professional training in motivational interviewing, as on many other topics, is often delivered via a one-time clinical workshop. To what extent do practitioners actually acquire skillfulness through such training? Twenty-two counselors participated in training, of whom 15 completed a study of changes in practice behavior up to 4 months after a motivational interviewing workshop. In addition to self-report questionnaires, they provided taped practice samples before and after training, which were coded for counselor and client behavior. On paper-and-pencil measures, participants reported large increases in motivational interviewing skills. Observational measures reflected more modest changes in practice behavior that were often retained 4 months after training. Clients, however, did not show the response changes that have been found to be predictive of better outcomes with motivational interviewing. While practice behavior changed to a statistically significant extent, the effect of training was apparently not large enough to make a difference in client response. Possible implications for training and quality control of psychotherapies are considered.