PURPOSE: To evaluate the morphological and radiographic features of hip instability in hip dysplasia. METHODS: Eighty-four patients who had ultrasonography for the assessment of hip instability and computed tomography scan for the assessment of bony morphology were included. The lateral center-edge angle (LCEA), vertical-center-anterior angle (VCA), acetabular roof obliquity (ARO), acetabular head index (AHI), and acetabular version angle (AVA) were calculated as pelvic parameters. Neck shaft angle (NSA), α-angle, femoral offset (FO), and femoral anteversion (FA) were obtained as femoral parameters. The combined anteversion angle (CAA) was defined as the sum of AVA and FA. RESULTS: Pelvic morphology analysis revealed that LCEA, VCA, and AHI were significantly lower, whereas ARO and AVA were significantly higher in the hip instability group. Furthermore, NSA, FO, and CAA were significantly higher in the hip instability group. The cutoff values for LCEA, VCA, and AHI were 17.6°, 34.7°, and 73.6%, respectively. Multivariate analysis revealed that LCEA and VCA were significantly associated with hip instability, with odds ratios of 1.57 and 1.56, respectively. Hip instabilities were associated with lateral/anterior/superior coverage deficiencies in the pelvis and with the NSA, FO, and CAA in the femur. Furthermore, a correlation between pelvic and femoral morphological parameters suggests that hip instability evaluations should include the evaluation of the anterior/lateral coverage of the acetabulum and femoral parameters. CONCLUSION: Our findings suggest that the LCEA, VCA, and AHI could serve as diagnostic markers for hip instability.