Nanometer circuits are becoming increasingly susceptible to soft-errors due to alpha-particle and atmospheric neutron strikes as device scaling reduces node capacitances and supply/threshold voltage scaling reduces noise margins. It is becoming crucial to add soft-error tolerance estimation and optimization to the design flow to handle the increasing susceptibility. The first part of this paper presents a tool for accurate soft-error tolerance analysis of nanometer circuits (ASERTA) that can be used to estimate the soft-error tolerance of nanometer circuits consisting of millions of gates. The tolerance estimates generated by the tool match SPICE generated estimates closely while taking orders of magnitude less computation time. The second part of the paper presents a tool for soft-error tolerance optimization of nanometer circuits (SERTOPT) using the tolerance estimates generated by ASERTA. The tool finds optimal sizes, channel lengths, supply voltages and threshold voltages to be assigned to gates in a combinational circuit such that the soft-error tolerance is increased while meeting the timing constraint. Experiments on ISCAS'85 benchmark circuits showed that soft-error rate of the optimized circuit decreased by as much as 47% with marginal increase in circuit delay.