Background. The purpose of this paper is to describe the frequency, pathophysiology and clinical sequelae of synovial plica of the knee. This structure is a remnant of tissue pouches found in the early stages of fetal growth. Symptomatic plica syndrome develops when the medial plica is irritated by injuries, an inflammatory state, or chronic overuse. Material and methods. We performed a retrospective analysis of the operative reports from 912 arthroscopies of the knee performed in the Orthopedic and Traumatology Department of Biziel Hospital in Bydgoszcz in the years 2002 and 2003. Results. Hypertrophic mediopatellar plica was found in 199 cases (21.8%). In 118 knees (12.9%) there were no more injuries except plica and associated chondromalacia of the patella and medial femoral condyle. Conclusions. On the base of this study we concluded that plica syndrome is an important clinical problem involving young people, especially women.