The invention relates to a balloon catheter, in particular for the widening of stents in fenestrations and for T-branch protheses, being provided with a balloon (4), a supply line in the catheter (2) leading to the balloon (4), which allows the balloon (4) to be pressurized, and a central lumen (3) for a guidewire, with the balloon (4) in the expanded state having at least two areas (P, D, M) of different diameter, with these areas merging into one another by forming a step.