INTRODUCTION: In total, there are fewer than ten reported cases of intraarticular ganglion cysts in the pediatric population. Herein, we report a rare case of intraarticular ganglion cyst inside the knee with extraarticular extension in a 5-year-old child. CASE PRESENTATION: A 5-year-old boy presented with an anterior knee mass associated with limping, and limited range of motion in the right knee for 1 year. Surgical excision with arthroscopy was performed to treat the intraarticular ganglion cyst with extraarticular extension. At follow-up, the mass had completely detached, and the patient had full range of motion without complaints or recurrence. CLINICAL DISCUSSION: Ganglion cysts are benign lesions, and are extremely rare in pediatric age groups with fewer than ten cases reported in the literature. We report this case as the first infrapatellar fat pad ganglion cyst with anterolateral extraarticular extension via the lateral reticulum, compared to previous reported cases, which were pure intraarticular cysts the majority of which had an ACL origin. CONCLUSION: The clinical manifestation of a rare ganglion cyst in the knee is variable. Magnetic resonance imaging is the cornerstone of diagnosis. Treatment varies according to the cyst location, and requires analysis of the mass, meticulous preoperative planning, and experienced surgeons.