To evaluate the root canal configuration of permanent mandibular first and second molar teeth in a Chinese subpopulation using cone-beam computed tomography (CBCT). Patients who required CBCT radiographic examinations as part of their routine examination, diagnosis and treatment planning, were enrolled. Cases where the anatomy was compromised by physiological or pathological processes and the original root canal morphology was not clear were excluded. A total of 389 healthy, untreated, fully developed mandibular molars in Chinese individuals were included. The following observations were recorded: (i) the number of roots and their morphology; (ii) the number of canals per root; (iii) the canal configuration; (iv) the frequency of distolingual roots in the mandibular first molars and (v) the frequency of C-shaped canals in the mandibular second molars. The root canal configurations were classified according to the method of Vertucci (Oral Surgery, Oral Medicine, and Oral Pathology58, 1984, 589). The majority of mandibular molars (70% of first molars, 76% of second molars) had two separate roots; however, three roots were identified in 29% of first molars. C-shaped roots occurred in 29% of second molars. Three canals were found in 56% of mandibular first molars and 43% had four canals. In the mandibular second molars, 46% had three canals and 38% had two canals. Most distal roots had a simple type I configuration, whereas mesial roots had more complex canal systems, with more than one canal. There were seven variants of the root canal morphology amongst the mandibular first molars and eight variants amongst the mandibular second molars, without considering the various root types. Three-rooted mandibular first molars and C-shaped mandibular second molars occurred frequently in this Chinese population. CBCT is an effective tool for the detection of additional distolingual roots and C-shaped roots/canals, and it is a valuable aid for dentists providing root canal treatment. © 2011 International Endodontic Journal.