Following surgical reduction of an irreducible hip in developmental dysplasia of the hip, imaging is required to ascertain successful reduction. Recent studies have compared MRI versus computed tomography (CT) in terms of cost, time, sensitivity and specificity. This is the first study to compare intraobserver and interobserver reliability for both modalities. Nineteen CT scans of 38 hips in 10 patients and nine MRI scans of 18 hips in six patients were reviewed on two separate occasions by three clinicians. Image clarity, confidence of diagnosis, time taken to perform the scan as well as radiation dose for CT were recorded. Intraobserver and interobserver reliability κ values were calculated. There were 14 female patients and one male patient. The mean age at the time of the scan was 12 months (range 3–25 months). Intraobserver reliability was greater than 0.8 (both CT and MRI). Interobserver reliability was greater than 0.8 (both CT and MRI). Image clarity was higher for CT for two out of the three clinicians (9.47 vs. 6.33 P<0.05; 9.89 vs. 8.11, P<0.05). All clinicians were equally confident in the diagnosis when using CT or MRI. The time taken to perform the investigation was not significantly different (3.32 vs. 4.88 min, P>0.05). The mean radiation dose for CT was 91.75 DLP (dose length product, mGy×cm) (95% confidence interval±26.95). Our results show that MRI is equal to CT as an imaging modality in the assessment of postreduction hips in developmental dysplasia of the hip. Intraobserver and interobserver reliability was excellent for both. The image clarity was higher for CT, but this method of imaging carries a significant risk of radiation exposure. We recommend that MRI should supersede CT as an imaging modality for this clinical situation.