Electrocardiogram abnormalities are reported to be complicated in Duchenne muscular dystrophy. Although Duchenne muscular dystrophy can be genetically diagnosed in young patients, extensive electrocardiogram studies have not been reported. Here, electrocardiogram abnormalities were examined in Duchenne muscular dystrophy cases with dystrophin gene mutations. Sixty-nine patients, aged </=18 years, received 136 electrocardiogram examinations. Sixty-four patients (91.3%) displayed one or more abnormalities. Furthermore, patients adolescent <10 years (84.8% of patients) displayed electrocardiogram abnormalities, and the most common abnormality was deep Q-waves. Remarkably, the abnormality incidence of both deep Q-waves and low RV5 + SV1 (R-wave V5 + S-wave V1) were significantly high in adolescent patients. Although the patterns or positions of dystrophin gene mutations were compared with electrocardiogram abnormalities, no predisposing mutation was disclosed. These results indicate that electrocardiogram abnormalities in Duchenne muscular dystrophy are a result of dystrophin deficiency, regardless of types of gene mutations. The disease can be divided into two types: age-dependent and age-independent. Deep Q-waves and low RV5 + SV1 are proposed as markers of age-dependent cardiac complications.