The purpose of this research was to study incidence; clinical, histological, and radiological features; and outcome of primary malignant giant cell tumor (PMGCT). The authors retrospectively reviewed all cases of giant cell tumor (GCT) in which a diagnosis of GCT was related to sarcoma treated in their department between 1997 and 2004. Three cases of PMGCT were found according to the criterion of Hutter and Dahlin. Histological and radiological records of all the three cases were reviewed. In these three cases of PMGCT, the initial clinical and radiological findings were the same as those for benign giant cell tumor. Wide excision of the tumor was performed in all three cases. In two cases, knee arthrodesis was performed, and in one case a custom-made total knee replacement was performed. PMGCT was diagnosed on initial biopsy in one patient, in the second patient it was diagnosed in the excised specimen, and in third case it was only diagnosed after local recurrence 6 months after initial treatment. All the patients died within 5 months of detection of recurrence and metastasis. PMGCT has a very poor prognosis. Histological examination is highly significant in such cases. Awareness about this entity, adequate biopsy, and sampling of specimen can aid in early diagnosis, which may improve the overall prognosis.