[en] The use of neo-adjuvant chemotherapy in the treatment of osteosarcoma has dramatically improved the survival rate in patients of osteosarcoma. Monitoring of preoperative chemotherapy response and estimating grade of tumor regression in patients with osteosarcoma is of pivotal importance before surgical removal of the tumor. The premise of the study was ¹⁸F-FDG whole body PET can be used to predict early the tumor response to chemotherapy and would help identifying unresponsive cases. The findings from this study provide evidence that amongst the patients with varying degree of disease burden at diagnosis, the FDG uptake in the primary lesion was higher in patient subgroup with distant metastasis as compared to those without metastasis or loco-regional metastasis. Thus SUVmax of the primary tumor may be directly correlated to the metastatic potential of the tumor. The study also emphasize on the need of the inclusion of PET in staging as well as restaging of the patients along with CT chest and MRI of the involved site. This helps not only in accurate staging but also helps in detecting new lesions by PET and detecting metabolically inactive lesions on PET. The study findings regarding assessment of response to chemotherapy by correlating % fall in Avg. SUV or SUVmax and % necrosis were statistically not significant but showed trend towards more reduction suggesting greater necrosis in the tumor whereas low post treatment SUVmax and ≥ 90% necrosis was consistent with the findings of the previous studies. Statistically significant result was not obtained which was believed because of small patient number in each subgroup