An 8-year-old girl presented to the orthopedics OPD with swelling and pain in the left knee for the past 6 months (Fig. 1a). The swelling had rapidly increased in size in the past 1 month. There was a history of difficult in walking and frequent locking of this knee. No history of trauma or any other joint involvement could be elicited. No similar history was found in siblings or mother. An X-ray of the knee joint was advised which showed a lytic lesion in the proximal tibial epiphysis with peripherally placed sclerotic areas (Fig. 2a). X-ray did not reveal any significant joint effusion and in view of marked joint swelling, a magnetic resonance imaging (MRI) of knee joint was done. The MRI showed a heterogeneous lesion in the tibial epiphysis with altered signal intensity and a sclerotic rim (Fig. 2b). The lesion involved the tibial spine with a breach of the articular margin. There was evidence of perilesional edema with soft tissue enhancement suggesting a reactive pathology. On the basis of the above two, a differential diagnosis of tuberculosis and chondroblastoma was suggested. The hematological and biochemical work-up of the patient was within normal limits. The joint aspirate was negative for any crystals. Mantoux test read 8 mm. In view of no evidence of tubercular etiology and provisionally neoplastic radiological diagnosis, the patient was taken up for excision of the lesion with bone grafting. The bone graft was taken from fibula. Intraoperatively, the synovium appeared markedly hyperplastic, yellowish in color, and extending into the supra and infrapatellar compartments of the knee (Fig. 1b). The lytic lesion was managed by intralesional curettage and packing with allograft bone chips along with excision of the hyperplastic synovium. The curetted material from the lytic lesion and synovial tissue were sent for histopathological examination. Sections from the synovial tissue showed villi-like proliferations of the hyperplastic synovium with expansion of the subsynovium with mature adipose tissue (Fig. 3a and b) and also seen were interspersed chronic inflammatory cells and few dilated vessels. Sections from the curetted tumor material showed a cartilaginous tumor composed of fragments of mature hyaline cartilage, compact polyhedral chondroblasts with well-defined cytoplasmic borders and hyperlobulated nuclei with grooves. A chicken-wire matrix surrounding the chondroblasts was seen (Fig. 3c and d). No nuclear pleomorphism or mitosis identified. A final diagnosis of chondroblastoma with synovial lipomatosis was given. The MRIs were reviewed and it was seen that the soft tissue enhancement was in real the thickened synovium thrown in finger-like projections. Postoperatively, the pain and joint swelling improved drastically and no recurrence is seen till date.