A Bouncy Knee is a knee control device for use in above-knee prostheses, designed to give a natural flex-extend action during the stance phase of the walking cycle. Tests with an adjustable device fitted to an amputee identified optimum angles of bounce (peak initial knee flexion after foot contact). Subsequently a clinical trial was conducted with six patients. The patients' gait was assessed using an instrumented walkway and polarized light goniometry. Symmetry of gait was improved in all cases and the patients reported a marked improvement in comfort and increased control in downhill walking. After removal of the units, cyclic testing was carried out without collapse of any Bouncy Knee unit. The clinical fitting procedure has been established and a simple peak-reading goniometer designed to enable the prosthetist fitting the unit to assess its performance. A production batch, suitable for Blatchford Modular Assembly Prostheses, Stabilised Knee users has been made.