A machine for packing cigarettes, having a group-forming device for forming a group of cigarettes, and a conveyor for feeding the group along a given path; the group-forming device has a number of seats, each for housing a respective subgroup of cigarettes; the subgroups are pushed, in use, through respective insertion channels tapering towards the conveyor, into a pocket of the conveyor to define the group of cigarettes; and the pocket has a substantially triangular cross section parallel to the path.