In this prospective randomised study two treatments after non-traumatic medial meniscal tear diagnosed with radiological examination and magnetic resonance imaging were compared; arthroscopic partial meniscectomy followed by supervised exercise or supervised exercise alone. The aim was to evaluate knee function and physical activity. Ninety patients (mean age 56 years) were evaluated using the Knee Injury and Osteoarthritis Outcome Score, the Lysholm Knee Scoring Scale, the Tegner Activity Scale and a Visual Analogue Scale for knee pain prior to the intervention, after 8 weeks of exercise and after 6 months. According to the outcome scores arthroscopic partial medial meniscectomy combined with exercise did not lead to greater improvement than exercise alone. After the intervention both groups reported decreased knee pain, improved knee function and a high satisfaction (P<0.0001). Forty-one per cent of the patients returned to their pre-injury activity level after 6 months. In conclusion, when evaluated with outcome scores, arthroscopic partial medial meniscectomy followed by supervised exercise was not superior to supervised exercise alone in terms of reduced knee pain, improved knee function and improved quality of life.