Becker muscular dystrophy: an unusual presentation.

A 15 year old boy who presented with passing painless dark urine was found to have myoglobinuria. His creatine phosphokinase was raised, and a muscle biopsy specimen showed non-specific dystrophic changes. Subsequent DNA analysis led to the diagnosis of Becker muscular dystrophy. Myoglobinuria may be a presenting symptom of Becker muscular dystrophy.