Abstract Accurate knowledge of root canal curvature is a critical factor in successful root canal procedures. The objective of this study was to determine the degree of root canal curvature and the frequency of curvature identified in different radiographic views in permanent incisors from a Chinese population. The curvature of canals from 299 permanent mandibular incisors was investigated by measuring the angle, the radius of curvature, and the length of the curved part of the canals. These measurements were taken by inserting size 10 K-files into the canals and taking radiographs of the tooth-file assembly from both facial and proximal views by using a standardized parallel technique. All radiographs were analyzed with a computerized digital image processing system. Statistical analysis was performed with analysis of variance test at α = .05. Of the 299 teeth examined, 252 (84.3%) were curved, and 125 (41.8%) of the teeth had secondary curvature. Curvature was most frequently detected in the proximal views rather than in the facial lingual views ( P < .05). The highest curvature among all samples tested was 44 degrees primary curvature and 36 degrees secondary curvature. The maximum and minimum radii of curvature for the sample set were 54.61 and 1.55 mm, respectively. The mean value of the radius of secondary curvature seen in proximal views was significantly less than that of the primary ones ( P < .05). The length of the curved parts of canals measured maximum and minimum values of 14 and 0.33 mm, respectively. It is suggested that the canal curvature can start at either the middle third or apical third of the tooth.