CASE: We present a unique case of bilateral ulnar longitudinal deficiency (ULD) with concurrent postaxial polydactyly (PAPD) in a 2-month-old boy, an association that has not previously been described. CONCLUSION: ULD, a rare musculoskeletal anomaly, often manifests with complex digital abnormalities. ULD may be associated with other musculoskeletal differences and congenital heart anomalies, necessitating comprehensive evaluation. Considering the Sonic hedgehog-Patched-Gli pathway's role in limb development, we discuss potential genetic mechanisms underlying this dual anomaly. This case broadens our understanding of ULD phenotypes and underscores the need for continued investigation regarding the genetic pathways underlying congenital upper limb differences.