Objective: To investigate the usefulness of diffusion-weighted magnetic resonance imaging (DWI) in odontogenic keratocysts, especially apparent diffusion coefficient (ADC) maps for the characterisation of normal structures and cystic lesions in the jaw. Methods: Sixteen patients who underwent magnetic resonance imaging (MRI) for the diagnosis of a cystic lesion in the jaw were included in this prospective study. DWI was performed on a 1.5 T unit with b factor of 0 and 800 s/mm2, and ADC maps were generated. ADC values were measured for the normal structures in the upper neck area and for the cystic lesion in the jaw. Results: The mean ADC value of the cerebrospinal fluid (3.66 ± 0.47 × 10-3 mm2/s) in the upper neck area was higher than that of the nasal mucosa (1.80 ± 0.19 × 10-3 mm2/s), Waldeyer's ring (0.75 ± 0.11 × 10-3 mm2/s) and the spinal cord (0.71 ± 0.20 × 10-3 mm2/s). The mean ADC value of the five odontogenic keratocysts (1.03 ± 0.31 × 10-3 mm2/s) was lower than that of the one simple bone cyst (2.79 × 10-3 mm2/s), three nasopalatine duct cysts (2.28 ± 0.12 × 10-3 mm2/s), three radicular cysts (1.82 ± 0.71 × 10-3 mm2/s) and four dentigerous cysts (1.67 ± 1.06 × 10-3 mm2/s). Conclusion: This study suggested the usefulness of DWI in odontogenic keratocysts, especially ADC maps for the characterization of normal structures and cystic lesions in the jaw. Keywords: magnetic resonance imaging (MRI), diffusion, cyst, odontogenic