The relations between blood glucose control (HbA(1c)), smoking, and health-related diabetes locus of control beliefs were studied in a consecutive adult sample of 187 patients with Type 1 diabetes who were free of diabetes complications. Those who were smokers (n=32) had poorer HbA(1c) values than non-smokers [7.5+/-1.4 (S.D.) vs 6. 8+/-1.2%, P=0.017]. When the patients were compared according to HbA(1c) quartiles, 17 of the smokers (53%) were found among those with worst blood glucose control. The smokers showed a lesser belief than the non-smokers in powerful others such as physicians and diabetes nurses in regards as diabetes control and the course of the disease [23.5+/-4.4 (S.D.) vs 25.8+/-5.5 (S.D.), P=0.05]. The group as a whole exhibited strong beliefs that their own behaviour was important for diabetes control. This belief appears incongruent with smoking behaviour. The results have implications for possible coping and defence strategies used by the smokers. Due to their worse blood glucose control, weaker beliefs in health care professionals, and possible denial-like coping strategies, smokers clearly need special attention in diabetes care, particularly in the view of their risk of developing long-term complications.