Aim - The main aim of this trial is to test the safety and efficacy of autologous stromal/stem cells, chondrocytes or the two combined in the treatment of knee cartilage defects. Patients & methods - Patients with symptomatic chondral/osteochondral defects will be randomized to cell therapy treatment with one of three cell populations (1:1:1). The primary efficacy outcome is a functional knee score (Lysholm) at 15 months post-treatment and the primary safety outcome is the incidence of adverse events. Secondary objectives are to analyze repair tissues, quality of life and cost-utility assessments. Exploratory objectives are to identify predictors for success/potency and dose-response relationships. Results & conclusion - This trial has been carefully designed so that valuable scientific and clinical information can be gathered throughout and in the final analysis.