The study determines the cost–utility of a unilateral electronic knee prosthesis (C-leg) compared to mechanical alternatives in trans-femoral amputees. For each type of prosthesis, 50 patients, treated in a major Italian centre, were enrolled. Quality adjusted life years (QALYs) were estimated from responses to EuroQol (EQ-5D). Healthcare and social costs were assessed for the estimated life cycle of the technologies (5 years). C-leg was associated with 0.09 more QALYs per patient per year (P = 0.007). For the 5-year period, the incremental cost–utility ratio of C-leg resulted in € 35,971 per QALY from the healthcare system perspective. If non-healthcare costs and productivity losses are included, the two groups to have similar costs (€ 66,669 vs € 66,927).