Whether or not there are gender differences in altruistic behaviour in Dictator Game experiments has attracted considerable attention in recent years. Earlier studies found women to be more altruistic than men. However, this conclusion has been challenged by more recent accounts, which have argued that gender differences in altruistic behaviour may be a peculiarity of student samples and may not extend to other groups. Here we study gender differences in altruistic behaviour and, additionally, in expectations of altruistic behaviour, in a sample of Amazon Mechanical Turk crowdworkers living in the US. In Study 1, we report a mega-analysis of more than 3, 500 observations and we show that women are significantly more altruistic than men. In Study 2, we show that both women and men expect women to be more altruistic than men. (C) 2018 Elsevier B.V. All rights reserved.