Background: Lower limb valgus alignment has previously been identified in pediatric patients with anterior cruciate ligament (ACL) rupture. This study aimed to evaluate knee morphology on magnetic resonance imaging (MRI) in valgus and non-valgus aligned pediatric patients with ACL rupture and compare them against a typically developed (TD) cohort without ACL rupture. Hypothesis: There would be differences in knee morphology between valgus and non-valgus aligned pediatric patients with ACL rupture and a TD cohort. Study Design: Cross-sectional study; Level of evidence, 3. Methods: Data were extracted from the Queensland Children's Hospital prospective pediatric ACL Injury Registry. Preoperative MRI of patients with ACL rupture was compared against an age- and sex-matched TD cohort without knee pathology. The following morphological parameters were measured: lateral femoral condyle index (LFCI), lateral tibial height, medial posterior slope, lateral posterior slope (LTS), medial tibial depth, and notch width index. The mechanical axis deviation (MAD) was measured from preoperative long-leg radiographs. One-way analysis of covariance with the Tukey post-hoc test compared parameters in valgus (MAD <1 mm medial), non-valgus (MAD ≥1 mm medial), and TD groups, adjusting for age and sex. Mean differences were reported with 95% CIs. Results: A total of 150 patients with ACL rupture were eligible. After propensity score matching against the TD cohort (n = 26), the ACL rupture group (valgus, n = 26; non-valgus, n = 26) had similar baseline characteristics: combined mean age (13.97 ± 2.20 years) and sex (57.69% women vs 42.31% men). Compared with the TD cohort, valgus ACL-ruptured patients had significantly smaller LFCI (–0.16 [95% CI, –0.20 to −0.11]) and larger LTS (2.53 [95% CI, 0.50 to 4.56]) values. Valgus-aligned patients with ACL rupture had smaller LFCIs compared with non-valgus-aligned patients with ACL rupture (–0.12 [95% CI, 0.17 to −0.08]). Conclusion: Compared with a TD cohort, morphological variations were found within subsets of pediatric patients with ACL rupture when accounting for lower limb alignment. Valgus-aligned patients had smaller LFCI and steeper LTS values than the TD cohort.