Magnetic resonance velocity mapping of intraaortic flow was performed prospectively in adolescents and adults after coarctation repair. The aims were to assess the feasibility and clinical usefulness of the technique in this patient group, and to study flow velocity distributions in repaired regions. Twenty consecutive patients attending for follow-up after repair of aortic coarctation, aged 15–39, mean 25 years, were studied using a 0.5 tesla Picker magnetic resonance machine. Spin echo and cine imaging with phase velocity mapping, echo time 3.6 ms, were used to study anatomy and flow in the repaired region. Transcutaneous ultrasonic examination, with continuous wave Doppler velocity measurement was performed independently on the same day. Velocity maps, acquired successfully in all patients, showed asymmetry and nonhomogeneity of flow in relation to anatomical distortions of repaired regions. Magnetic resonance and Doppler measurements of peak velocity compared as follows: n=20, range 1.2–3.9 m/sec, mean 2.33 m/sec, mean of differences (Doppler-MR) 0.22 m/sec, standard deviation of differences ±0.27 m/sec. Localized velocity peaks adjacent to wall deformations were identified by magnetic resonance in five patients without significant restenosis. Magnetic resonance imaging with velocity mapping proved reliable and informative in follow-up assessment in adolescents and adults after surgical repair of aortic coarctation. There was satisfactory agreement between magnetic resonance and Doppler measurements of peak velocity. Velocity maps showed that localized velocity peaks may occur in limited parts of the stream adjacent to distorted aortic boundaries without stenosis. This could be a cause of overestimation of pressure gradients from peak velocity data, a possibility which requires further investigation.