The role of constitutional courts in deeply divided societies is complicated by the danger that the salient societal cleavages may influence judicial decision-making and, consequently, undermine judicial impartiality and independence. With reference to the decisions of the Constitutional Court of Bosnia-Herzegovina, this article investigates the influence of ethno-national affiliation on judicial behaviour and the extent to which variation in judicial tenure amplifies or dampens that influence. Based on a statistical analysis of an original dataset of the Court's decisions, we find that the judges do in fact divide predictably along ethno-national lines, at least in certain types of cases, and that these divisions cannot be reduced to a residual loyalty to their appointing political parties. Contrary to some theoretical expectations, however, we find that long-term tenure does little to dampen the influence of ethno-national affiliation on judicial behaviour. Moreover, our findings suggest that this influence may actually increase as a judge acclimates to the dynamics of a divided court. We conclude by considering how alternative arrangements for the selection and tenure of judges might help to ameliorate this problem.