The Ehlers-Danlos syndromes (EDS) are a rare group of connective tissue disorders characterized by severe joint hypermobility and instability. Ten patients with 12 primary knee arthroplasties were identified. Average age at time of surgery was 43.3 years, with follow-up data acquired at an average of 65 months after surgery. Primary indications for surgery were tibiofemoral or patellar instability (n = 8) and arthritis (n = 4). Knee Society Functional scores averaged 29.6 before surgery and 51.3 at time of interview (P<.005). Knee Society Knee scores at time of follow-up evaluation averaged 70. Tibiofemoral and patella stability were significantly improved. Arthroplasty appears to be an effective option for knee arthritis and instability in EDS patients, although results and satisfaction are lower than that reported for conventional arthroplasty indications.