Aim: To make dentists and pedodontists aware of a possible outcome of a rapidly growing swelling. Background: Ewing's sarcoma is a rare aggressive variant of small round cell tumors and is an uncommon malignancy that occurs usually in childhood. It constitutes 10–15% of all primary malignant tumors and represents the second most common malignant bone tumor occurring in children and young adults. Case description: We report a case of Ewing's sarcoma in an 11-year-old male child who reported with a rapidly progressing swelling in the left mandibular posterior region. Panoramic view and computed tomography showed characteristic moth eaten and sun-ray appearance. Fine-needle aspiration cytology revealed a small round cell tumor. Since the exact diagnosis is hard to achieve before biopsy, the condition poses a difficult diagnostic dilemma for the clinician. Histopathology was performed for the accurate diagnosis. Conclusion: Dentists and pedodontists should develop a high index of suspicion in diagnosing cases with rapidly enlarging intraoral or extraoral swellings as early and correct diagnosis may improve clinical management and survival for patients with this disease. Clinical significance: Our case report is an attempt to help the dental community in developing familiarity with the clinical presentation of Ewing's sarcoma.