We investigate the influence of group size and gender composition on collective ethical desicion-making. In an online experiment, groups of 2, 3, 4, or 5 persons have to report unanimously the outcome of a die roll, which determines their monetary payoff. Each composition with respect to the number of men and women in a group is equally likely within each group size. The members of a group see the same video and interact in a video chat. Moreover, we elicit a set of social preferences, a measure of individual honesty, a measure of cognitive ability, and a measure of social cognition.