Mycoplasma pneumoniae pneumonia (MP) is responsible for 10-40% of cases of pediatric community-acquired pneumonia. Occasionally, progression to severe pneumonia occurs despite appropriate antibiotic therapy. We retrospectively evaluated the effect of prednisolone in 15 children with MP whose clinical and radiographic course worsened despite broad-spectrum antibiotics, including appropriate macrolides. The mean (+/- SD) age was 6.1 +/- 1.9 years, and 10 were boys. All children had received macrolides at presentation, but they had persistent fever and progressively worsening radiographic findings. In addition to broad-spectrum antimicrobial therapy, we added prednisolone (1 mg/kg for 3-7 days, then tapered over 7 days) on day 6 ( 1.5 days) of admission. Fourteen children became afebrile within 24 hr, and their clinical status and radiographic findings improved over several days. The white blood cell count at presentation was 7,500 +/- 2,000/mm(3), with a proportion demonstrating lymphopenia (lymphocyte differential, 19.7 +/- 5.7%). In conclusion, corticosteroid treatment appeared to be temporally associated with clinical and radiographic improvement, and may be helpful for reducing morbidity in children with macrolide-nonresponsive severe MP Further studies may be warranted.