OBJECTIVE: To present normative data on prenatal mandibular morphology and growth. MATERIAL AND METHODS: Fifty-four normal fetuses (Danish Caucasian) were included in the study (gestational age: 11-26 weeks). Fetuses were scanned using a GE Voluson 730 Expert 3D scanner. Scans were visualized and analyzed using GE 4DVIEW software. Mandibular dimensions [base length (B), ramus height (H), and total length (L)] and the mandibular angle (phi) were measured, and the mandibular index was calculated. Method error was estimated by duplicate measurements. Growth was calculated by regressing measured variables on age. RESULTS: Mandibular measurements were found to be reliable [precision: 0.5-1.2 mm (1SD)]. Mean mandibular variable values at week 11: B = 5.2 +/- 2.5 mm; H = 2.7 +/- 1.3 mm; L = 7.7 +/- 3.2 mm; phi = 149 +/- 6.0 degrees; and at week 26: B = 22.6 +/- 2.5 mm; H = 12.3 +/- 1.3 mm; L = 33.1 +/- 3.2 mm; phi = 135 +/- 6.0 degrees. A linear model described growth (B(g)/H(g)/L(g)/phi(g)) giving B(g) = 1.2; H(g) = 0.64; L = 1.7 mm/week; phi(g) = - 0.9 degrees/week. CONCLUSION: Normative 3D data values for the human mandible in 11- to 26-week-old fetuses were presented. All measured mandibular parameters could be described using a linear increasing model from 11 to 26 weeks. All linear dimensions increased in size, while the mandibular angle decreased steadily during the observation period.