The present study evaluated the long-term prognosis of tunnel preparations performed in a large number of teeth with advanced periodontal furcation defects. One hundred seven (107) patients, in which 156 teeth had been treated by tunnel preparations, were recalled for an evaluation, which was based on a questionnaire, a clinical examination, and radiographs; 102 patients attended (149 teeth = 95%). The mean observation time per tooth was 37.5 months (range 10 to 107 months). The results showed that 10 teeth (6.7%) had been extracted and 7 teeth (4.7%) hemisected. The indication for 12 of these extractions or hemisections was root caries. Among the remaining 132 teeth, 23 (15.4%) showed initial or established caries. There was no relationship between caries development and length of the observation time. Thus, approximately 75% of the teeth were still caries-free and in function. The findings demonstrated that tunnel preparations have a considerably better prognosis than previously reported and should be considered a valid treatment alternative.