Purpose: An attempt to define recurrent implantation failure.
Methods: Literature review.
Results: Numerous definitions of recurrent implantation failure exist. The complexity and redundancy of the process of implantation makes a single definition difficult to determine.
Conclusion: Each center must establish a definition of recurrent implantation failure based upon the data from that center. The definition of RIF used in our program requires the transfer of > or = 8, 8-cell stage embryos or > or = 5 blastocyst embryos.