Two levels of aligned stencil lithography were used to fabricate pentacene thin film transistors on 12 mu m thick flexible polyimide substrates. Flexible transistors with 20 x 40 mu m(2) channels were electrically measured under strain up to 2.6%. After one stretching cycle, their average mobility was decreased by 21%, remaining constant after the next 100 cycles. In order to decouple ageing from stretching effects for long-term cycling, transistors with 10 x 20 mu m(2) channels were stretched up to 28,000 times and measured in the relaxed state, in parallel with reference samples left on the wafer. Their mobility decreased by 25% after the first cycle, while the consequent stretching did not affect the mobility more than natural ageing. (C) 2012 Elsevier B.V. All rights reserved.