['Mesenchymal stromal cells (MSC) are gaining in popularity as an experimental therapy for a number of conditions that often require expansion ex vivo prior to use. Data comparing clinical-grade MSC from various ages of donors are scant. We hypothesized that MSC from older donors may display differences in cellular fitness when expanded for clinical use.', 'We evaluated the expression of several markers of aging, oxidative stress and growth kinetics, and telomere length, in MSC obtained from a wide age range (8 months to 58 years).', 'To evaluate cellular fitness we compared MSC expanded from younger (8 months-6 years) versus older (38-58 years) donors in terms of selected cell-surface markers, lipofuscin, migration ability, telomere length and expression of iNOS, PGE₂, p16INK and SOD. Results did not differ between these groups. Neither SOD activity (0.025 versus 0.028 U/mL) nor death after oxidative challenge was significantly different (1% versus 1.5%, P = 0.14). We did find that, although MSC from older individuals produced slightly fewer cells over a 28-day culture period and had a slightly longer doubling time (54 h versus 42 hr, a satisfactory clinical product could still be obtained regardless of age cohort.'] Are mesenchymal stromal cells from donors varying widely in age of equal cellular fitness after in vitro expansion under hypoxic conditions?