Juvenile dermatomyositis (JDM) is the most common myopathy in children with characteristic skin rash and muscle weakness, in which longer duration of untreated disease was associated with less muscle weakness. The duration of untreated inflammation may alter the apoptotic pathways involved in skeletal muscle damage. Diagnostic muscle biopsies from 14 untreated patients were stained for apoptosis markers. TUNEL-positive nuclei and caspase 3 were detected within the laminin layer, indicating apoptosis of skeletal muscle nuclei. Untreated JDM disease duration greater than 2 months ("long"), was associated with higher Fas-positive cell counts in the perivascular region compared with the "short" disease duration group, 2 months or less. Within the "long" duration group, higher Fas-positive cell counts were positively associated with increased TUNEL-positive nuclei and caspase 3. We conclude that the duration of untreated disease (chronic inflammation) influences the mode of continuing cell damage and death in children with JDM.