Human reproduction appears to be an inefficient process, primarily because of chromosome errors in gametes and the resultant embryos. This chapter discusses the cytogenetic factors involved in miscarriage in the general population and in couples with recurrent pregnancy loss. It reviews the process of meiosis in gametogenesis and highlights the importance and limitations of cytogenetic analyses of miscarriage tissue. Recently, recurrent aneuploidy has been suggested as a factor associated with a history of recurrent pregnancy loss. Cytogenetic analyses can be performed on miscarriage tissue using several techniques, including cell culture followed by chromosome banding, microsatellite testing and comparative genomic hybridization. Comparative genomic hybridization followed by flow cytometry may prove a powerful technique to provide chromosome results on paraffin-stored miscarriage tissue. The possibility of recurring chromosome errors as etiologic for recurring pregnancy loss, has led to the recent application of pre-implantation genetic screening (PGS) for management of idiopathic recurrent miscarriage.