Wiedemann-Steiner syndrome is a rare genetic disorder characterized by short stature, hairy elbows, facial dysmorphism, and developmental delay. It can also be accompanied by musculoskeletal anomalies such as muscular hypotonia and small hands and feet. Mutations in the KMT2A gene have only recently been identified as the cause of Wiedemann-Steiner syndrome; therefore, only 16 patients from 15 families have been described, and new phenotypic features continue to be added. In this report, we describe 2 newly identified patients with Wiedemann-Steiner syndrome who presented with variable severity. One girl exhibited developmental dysplasia of the hip and fibromatosis colli accompanied by other clinical features, including facial dysmorphism, hypertrichosis, patent ductus arteriosus, growth retardation, and borderline intellectual disability. The other patient, a boy, showed severe developmental retardation with automatic self-mutilation, facial dysmorphism, and hypertrichosis at a later age. Exome sequencing analysis of these patients and their parents revealed a de novo nonsense mutation, p.Gln1978*, of KMT2A in the former, and a missense mutation, p.Gly1168Asp, in the latter, which molecularly confirmed the diagnosis of Wiedemann-Steiner syndrome.