OBJECTIVE:To evaluate the effectiveness of a nurse-managed smoking cessation intervention in diabetic patients. RESEARCH DESIGN AND METHODS:This randomized controlled clinical trial involved 280 diabetic smokers (age range 17-84 years) who were randomized either into control (n = 133) or intervention (n = 147) groups at 12 primary care centers and 2 hospitals located in Navarre, Spain. The intervention consisted of a 40-min nurse visit that included counseling, education, and contracting information (a negotiated cessation date). The follow-up consisted of telephone calls, letters, and visits. The control group received the usual care for diabetic smokers. Baseline and 6-month follow-up measurements included smoking status (self-reported cessation was verified by urine cotinine concentrations), mean number of cigarettes smoked per day, and stage of change. RESULTS:At the 6-month follow-up, the smoking cessation incidence was 17.0% in the intervention group compared with 2.3% in the usual care group, which was a 14.7% difference (95% CI 8.2-21.3%). Among participants who continued smoking, a significant reduction was evident in the average cigarette consumption at the 6-month follow-up. The mean number of cigarettes per day decreased from 20.0 at baseline to 15.5 at 6 months for the experimental group versus from 19.7 to 18.1 for the control group (P < 0.01). CONCLUSIONS:A structured intervention managed by a single nurse was shown to be effective in changing the smoking behavior of diabetic patients.