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Potato is adapted to mild climates, but climate change may increase its exposure to more high temperature episodes of greater severity. However, there is limited information on the likely response of potato to high temperature episodes. We investigated the growth of potato exposed to an episode of high temperature before (Expt. 1) or after tuber initiation (Expt. 2). In both glasshouse experiments, plants were grown at 22 degrees C. At 35 days after planting (DAP) (Expt. 1) or 43 DAP (Expt. 2), plants were transferred to high temperature treatments of 26 or 30 degrees C for nine days then returned to 22 degrees C for 26 days. Tuber dry matter was reduced to a similar extent whether the high temperature episode occurred before or after tuber initiation. These effects were inconsistent with previously proposed mechanisms that attributed reduced tuber dry matter to starch synthase inhibition or increased gibberellic acid production. They were more consistent with insufficient whole plant carbon occasioned by reduced leaf area and continued shoot growth, particularly of the laterals, during and after the high temperature episode. Starch and sucrose distribution in the plants supported this but also suggested different mechanisms when the high temperature occurred before or after tuber initiation.