A 16-year-old boy developed left foot pain of unknown cause that was 
unresponsive to conservative treatment, associated with fever and difficulty 
walking. He was admitted to our hospital with osteomyelitis of the accessory and 
body of the navicular bone. Surgery could not be performed because the patient 
had been diagnosed with Wiskott-Aldrich syndrome. After antibiotic therapy, 
laboratory abnormalities and pain had resolved. One year after treatment, the 
patient had returned to his original level of sports activity. Both an accessory 
navicular and the body of the navicular bone may develop osteomyelitis in 
immunocompromised patients; early diagnosis is important for prescribing 
effective conservative treatment.