BACKGROUND: There is widespread belief that adding smoking status to the list of vital signs in medical practice will lead to an increased likelihood that physicians will offer more cessation support for smokers during office visits. This article evaluates the impact of introducing routine use of smoking status as a vital sign on clinician cessation support in a primary care setting. METHODS: A total of 429 adult health plan members who were smokers and recent quitters from 2 primary care clinics in Minneapolis, Minn, were administered a 28-item questionnaire by telephone. The instrument included questions about patient health status, smoking status, advice about smoking, clinic actions during the most recent visit, satisfaction with clinic actions, and intention to change smoking. Comparisons were made with a cohort of smoking patients before and after smoking status was used as a vital sign, using 2-tailed t tests for continuous variables and chi-square analysis for categorical variables. RESULTS: Patient self-report of receiving advice about smoking in the past year (about 66%) was unchanged after smoking status was implemented as a vital sign. Medical chart documentation of tobacco use increased from 38.0% to 78.4% of all encounters, whereas documentation of advice about smoking decreased from 33.5% to 18.8%. Except for identification of tobacco use before implementation of the guideline, none of the specific activities recommended in the guideline occurred at very high levels. CONCLUSION: Implementing smoking status as a vital sign appears to have increased the documentation of tobacco use but had little effect on specific implementation actions. Overall, the findings suggest that more consistent identification of tobacco use alone will not lead to guideline-recommended changes in cessation support actions by clinicians. Greater environmental changes will be needed if tobacco guideline goals are to be achieved.