The purpose of this study was to explore the difference between congruency and incongruency of the first metatarsophalangeal (MTP) joint in hallux valgus using weight-bearing CT (WBCT) and to identify the risk factors for incongruency. From January 2019 to January 2021, WBCT scans were retrospectively analyzed for 110 (191 feet) consecutive patients. According to whether the metatarsal articular surface and phalanx articular surface were parallel, they were divided into congruency (73 feet) and incongruency groups (118 feet). The age, intermetatarsal angle (IMA), hallux valgus angle (HVA), distal metatarsal articular surface angle (DMAA), first metatarsal coronal pronation angle (α angle), tibial sesamoid 7 positions (TSP), and tibial sesamoid coronal grading (TSCG) were compared between the two groups. Binary logistic regression was used to analyze the influencing factors of incongruency. Receiver operating characteristic (ROC) curve analysis was applied to determine the cutoff value. There were significant differences in IMA, HVA, DMAA, α angle, age, TSP, and TSCG between congruency and incongruency groups (P<0.05). Binary logistic regression analysis showed that TSCG, HVA, α angle were the influencing factors of incongruency. ROC curve analysis demonstrated that the cutoff values for incongruency were 1 position for TSCG (sensitivity:0.835; specificity:0.884) with the area under curve (AUC) of 0.892, 30˚ (sensitivity:0.795; specificity:0.812) for HVA with the AUC of 0.878, and 24° (sensitivity:0.530; specificity:0.797) for α angle with the AUC of 0.686. Incongruency of the first MTP joint indicated a more severe hallux valgus, and was associated with increased HVA, α angle, and TSCG. Level of Evidence: 3.Copyright © 2023. Published by Elsevier Inc.