The proposed study is a single center, unblinded, non randomized, phase I/II trial in which the patients will be treated with a single dose of autologous stromal vascular cells (SVF) isolated from 500 ml of adipose tissue extracted from the infraumbilical area. The cellular product will be administered via intra-articular injection into patients with moderate to severe osteoarthritis (OA). Administration will be performed by injection into the synovial space. The dosing regimen will consist of two intraarticular injection of autologous SVF into the index knee. Total injection volume will be about 30 mL in two 15 mL aliquots via a 23 gauge needle inserted 1.5 cm. deep into the intraauricular space of the knee. The total number of SVF to be injected is 1.0 x 10(7) to 5 x 10(7).