This paper deals with the design of helical gears that have minimum transmission error and@ at the same time@ are less sensitive to manufacturing errors. The paper addresses two stages in design: 1) Design generation stage where feasible designs are generated for a given specification and 2) Design of profile and lead modifications that minimize transmission error and its sensitivity to manufacturing errors. The paper presents a brief discussion on how one can effectively minimize transmission error in helical gears by combining both lead and profile modifications.