Objective: Multirooted teeth respond less favorably to non-surgical periodontal treatment and long-term tooth prognosis is influenced by the degree of furcation involvement (FI). Therapeutic strategy for multirooted teeth is essentially based on accurate diagnosis of the FI. The aim of this systematic review is to evaluate the accuracy of the different furcation assessment methods and to determine if radiographic help is needed to determine early stage of FI. Methods: Electronic databases were searched up to March 2021. Comparative studies describing the reliability of different clinical and/or radiological furcation assessment methods were identified. Results: A total of 22 studies comparing at least 2 furcation assessment methods, among which 15 retrospective studies, 5 prospective studies, 1 randomized controlled trial and 1 case series, were included in this review. The reliability of cone beam CT (CBCT), intraoral radiographs (IOs), orthopantomograms (OPGs) and MRI to identify FI was evaluated. Using OFS as a reference for FI detection and diagnosis, agreement ranged from 43.3 to 63% for OPG, 38.7 to 83.1% for IO and 82.4 to 84% for CBCT. The validity of the measurements was mainly influenced by the location of the furcation entrance. For radiological diagnosis, CBCT displayed the closest agreement with OFS while the accuracy of IO and OPG showed modest agreement and were influenced by the examiner’s experience. Conclusion: Altogether, it appears that the use of IO, OPG or CBCT allows detection of FI but could not be considered as gold-standard techniques.