Although synovial plicae of the knee are frequently observed in adults and often bilateral, they remain, in most cases, asymptomatic. Pain is thus the most commonly encountered symptom. We report the case of an unusual complete suprapatellar plica of pseudotumoral aspect. Suprapatellar plicae account for 58 to 87% of all plicae of the knee and mostly remain asymptomatic except in case of a complete septum. A 17-year-old male presented with complaints of his right knee with local discomfort for more than one-year duration. The pain mostly arose following a prolonged sitting position but with no significant pain in the knee otherwise. The presence of an anterolateral suprapatellar mass at clinical examination required the need for further tests (standard X-rays and MRI). On MR imaging, the liquid aspect of this mass associated with a complete suprapatellar bandlike structure separating the sub-quadricipital recess from the knee joint suggested the diagnosis of a complete septum type of suprapatellar plica. Treatment consisted in an arthroscopic resection. Anatomopathologic verification of the removed tissues confirmed the benignant nature of this resected material. Outcome was favourable with disappearance of the knee discomfort and suprapatellar septum.