Aneurysmal bone cysts are rare benign bone tumours that were first described by Jaffe and Lichtenstein in 1942. They account for 1% of all biopsied primary bone tumours and appear as rapidly growing destructive lesions that expand the cortices. ABC can exist either as a primary bone lesion (70%) or as a secondary lesion when a preexisting osseous lesion can be identified (30%). A 4 years old male child present with a progressive swelling over proximal part of right arm for last 10 months. For last 3 months it rapidly increased in size, accosiated with throbbing pain. X ray shows Expansible lytic lesion, loculated appearance, cortical break and metaphysical lesion over proximal humerus. Histopathology report shows ANEURYSMAL BONE CYST. Exicision of whole mass with free fibular graft done under general anesthesia. Union at both ends of the fibular graft and over head hand movement possible at 8 month follow up. Complete re-modelling and reappearing of epiphysis with acceptable range of movement of upper limb seen after one year six month follow up.