Objectives: Evaluation of tooth loss of molars in relation to their degree of furcation involvement (FI) and treatment modality in patients maintained over a period of at least five years after corrective periodontal therapy. Material and Methods: This study evaluated 70 patients (mean age 46 years; 40 females) to determine the relationship of loss of molars to the degree of FI (degree 0, I, II, III) and periodontal therapy (no further therapy, non-surgical and surgical scaling and root planing, access flap, tunnel preparation, resective or regenerative therapy). The following criteria were required for inclusion: periodontal therapy of at least one molar, at least 5 years of supportive periodontal therapy (SPT), baseline clinical or intrasurgical assessment of the FI. Results: At baseline of periodontal therapy the 70 patients presented a total of 501 molars; 243 were located in the maxilla and 258 in the mandible; 195 exhibited no FI, 119 degree I, 122 degree II, and 65 degree III FI. Only 27 molars did not receive any further periodontal treatment; 126 molars were subjected to non-surgical therapy, and 230 to flap-surgery. Tunnel preparation was performed in 12 molars, root-resection in 18, and regenerative therapy in 56 teeth. 32 molars were extracted during active periodontal therapy (APT): 7% without FI, 3% with degree I, 2% with degree II, and 20% of the molars with degree III FI. The mean follow-up period was 77 months. In this period further 27 molars were lost. Molars with degree III FI had the highest mortality (36%; APT: 22%, SPT: 14%). 16 out of a total of 21 extracted molars with a baseline degree III FI were maxillary teeth. Conclusion: After therapy, the prognosis of molars with baseline degree I and II FI was similar to that of molars without FI. Mandibular molars with degree III FI revealed to have a better prognosis than maxillary molars with degree III FI. Keywords: furcation involvement, molars, periodontal treatment, tooth loss, long-term stability