Osteoarthritis is the most often joint disease characterized by changes in the joint cartilage and later also in other joint structures. It is the most common cause of functional impairment of the locomotor system. It can be primary or secondary. It appears after the age of 40 or 50. Factors that contribute to development of osteoarthritis of the knee are genetic factors, obesity, mechanical factors, age in general, while the symptoms that characterize it are pain, swelling, stiffness and muscle weakness. Knee osteoarthritis is treated conservatively and surgically. Conservative treatment includes physical therapy which is of great importance. If conservative treatment is unsuccessful, osteoarthritis is treated surgically. Operative options for knee osteoarthritis include arthroscopy, corrective osteotomy, knee PEP, knee TEP and arthrodesis. Physiotherapy assessment is important for planning rehabilitation and for comparing and evaluating the results obtained after rehabilitation. The physiotherapist documents the physiotherapeutic evaluation according to the SOAP model, where the subjective examination is an interview with the patient and the objective examination collects data through observation, palpation, measurements and tests for osteoarthritis. Physiotherapy procedures in the treatment of knee osteoarthritis include therapeutic exercise, electrotherapy, laser therapy, magnetotherapy, cryotherapy, thermotherapy and hydrotherapy. Also, the role of the physiotherapist is very important in the education of a patient suffering from knee osteoarthritis.