The purpose of this review was (i) to conduct a literature review on the prevalence and morphologic classification of mandibular first molars with disto-lingual (DL) roots, and (ii) to discuss the clinical approach to diagnosis and root canal treatment of these teeth. A search was carried out on electronic (MEDLINE, PubMed and Cochrane) and hand databases, which covered all publications from 1970 to December 2011. Two reviewers independently assessed the studies and recorded type of study, origin and sample sizes, number of teeth with three roots and type of root canal configuration. Forty-five studies were identified with a total of 19,056 mandibular first molar teeth. The frequency of DL roots was 14.4% and was associated with certain ethnic populations. The most common canal configuration of mesial and distal roots was Vertucci types IV and I, respectively. No significant differences were observed in the prevalence of DL roots according to gender. Variable results related to side were observed as well as a trend in bilateral occurrence. The root length of the DL roots was in general shorter than that of the disto-buccal roots (DB). Most DL roots had a greater angle of curvature and a smaller radius of curvature in a bucco-lingual orientation. The best methods to identify DL roots are a 25° mesial parallax periapical radiograph or cone-beam computed tomography (CBCT). A trapezoidal shape access cavity is desirable to locate the orifice of the DL canal. Clinicians should be aware of the variable furcation levels during coronal pre-flaring or post-space preparation to avoid furcal/strip perforations and a weakening of DL roots.