OBJECTIVE To determine whether a new assisted hatching (AH) method increases the implantation and clinical pregnancy rates of frozen-thawed day-3 (D3) embryos. METHODS Prospective study. METHODS A university hospital in vitro fertilization (IVF) program. METHODS Patients who had their first IVF/intracytoplasmic sperm injection (ICSI) cycles between June 1, 2006, and December 31, 2008, with fresh IVF-embryo transfer failures or without fresh embryo transfer. METHODS The couples were randomized into thawed embryo transfer after AH versus no AH. In the AH group, the zona pellucida (ZP) of D3 frozen-thawed embryos was expanded by injected hydrostatic pressure after thawing. In the control group, embryos were pierced by ICSI needles without expanding the ZP. METHODS Clinical pregnancy and implantation rates. RESULTS The morphologic features of the blastomeres were carefully monitored and recorded. In the AH group, 244 embryos were thawed, and 178 (73.0%) survived; in the control group, 259 embryos were thawed, and 190 (73.4%) survived. Despite the transfer of a similar number of embryos, the AH group resulted in statistically significantly higher implantation and clinical pregnancy rates compared with the no AH group. CONCLUSIONS Mechanically expanding the ZP of frozen-thawed D3 embryos with injected hydrostatic pressure after thawing increases the implantation rate compared with control embryos.