We report a case of Langerhans cell histiocytosis (LCH) occurring in the pelvis of a 2-year 11-month-old female with fluid-fluid level seen on MRI. Aspiration of the fluid during biopsy showed it to be blood with a few inflammatory cells and eosinophils. Tissue obtained during the biopsy confirmed the diagnosis to be LCH. While fluid-fluid levels have been infrequently encountered in skull lesions due to LCH, they have yet to be reported in lesions of the appendicular skeleton. The aim of this report is to familiarize radiologists with the fact that fluid-fluid levels can occur in LCH of the appendicular skeleton in children.