BACKGROUND: Facioscapulohumeral muscular dystrophy (FSHD) is associated with contractions of the polymorphic D4Z4-repeat array in 4q35 and has the distinctive clinical presentation of an initial involvement of the facial, shoulder-girdle, and upper-arm muscles. The aim of the present study was to determine clinical characteristics in Korean patients with FSHD and potential relationships between contracted D4Z4-repeat size and the FSHD phenotype. METHODS: We studied 34 genetically confirmed patients who had repeat sizes less than 38 kb, and analyzed their clinical manifestations with a structured protocol. The expressed phenotypes were scored according to the Clinical Severity Score formulated by Ricci and van Overveld. RESULTS: The clinical spectrum ranged widely, from asymptomatic individuals with minimal signs to wheelchair- bound patients. The initial affects were mainly in the facial muscles (68.8%), followed by the shoulder-girdle muscle (28.1%). Asymmetric features of the face and shoulder girdle were also important findings (71.9% and 90.0%, respectively). Winging scapular (87.5%), transverse smile (84.4%), Beevor's sign (68.8%), and sleeping with eyes opened (59.4%) were clinically important signs. There was a significant negative correlation between repeat size and clinical severity (r=-0.38, p=0.03). CONCLUSIONS: Distinctive clinical characteristics of FSHD are descending progression and asymmetric distribution of the muscle weakness. Our results also confirmed that the severity of FSHD increases with decreasing D4Z4-repeat size.