Background Evaluation of fetal central nervous system (CNS) agenesis by ultrasonography (US) is frequentlylimited, but magnetic resonance imaging (MRI) has its own advantages and is gaining popularity in displayingsuspected fetal anomalies. The purpose of this study was to explore the value of MRI in detecting fetal CNSagenesis.Methods Thirty-four women (aged from 22 to 35 years, average 27 years) with complicated pregnancies (16-39 weeks of gestation, average 30 weeks) were examined with a 1.5 T superconductive MR unit within 24 hoursafter ultrasonography. Half-Fourier acquisition single-shot turbo spin-echo (HASTE) T2-weighted imaging (T2WI)sequence were performed in all patients, and fast low angle shot (FLASH) T1-weighted imaging (T1WI) sequencewere applied sequentially in seven of them. Comparison of the results was made between the MRI and USfindings as well as autopsy or postnatal follow-up MRI findings.Results The gyrus, sulcus, corpus callosum, thalamus, cerebellum, brainstem, and spinal cord of fetus wereshown more clearly on T2-weighted MR images than on T1-weighted MR images. MRI corrected the diagnosis ofUS in 10 cases (10/34, 29.41%) and the diagnosis was missed only in 1 case (1/34, 2.94%).Conclusion MRI has advantages to US in detecting fetal CNS anomalies and is a supplement to US incomplicated pregnancies.