Background: Adipose tissue-derived mesenchymal stem cells (ASCs) can be isolated from subcutaneous fat harvested by tissue resection or liposuction. Objectives: The authors compared ASCs isolated by tissue resection or power-assisted liposuction (PAL) to determine whether either surgical procedure yielded ASCs with improved purity and competence that was preserved for several passages. Methods: For this experimental study, ASCs were isolated from fat harvested by tissue resection or PAL from six patients who underwent abdominoplasty. ASCs were counted to determine cell yields, and viabilities were assessed with an amine-reactive dye and by fluorescence-activated cell sorting (FACS). Cell phenotypes were determined by immunostaining and FACS, and doubling times were calculated. Senescence ratios of the cells were detected by gene profiling and by assaying â-galactosidase activity. Multipotency was evaluated by induced differentiation analyses. Results: No significant differences were observed in cell numbers or viabilities of ASCs isolated following either surgical method of fat harvesting. Both populations of cultured ASCs expressed markers of mesenchymal stem cells and preserved this expression pattern through the third passage. PAL and tissue resection yielded ASCs with similar division rates, similar senescence ratios into the fourth passage, and similar capacities to differentiate into osteocytes or adipocytes. Conclusions: Fat harvested by PAL or tissue resection yielded uniform cultures of ASCs with high division rates, low senescence ratios, and multipotency preserved into passages 3 and 4. Because PAL is less invasive, it may be preferable for the isolation of ASCs.