The elaboration of a quality oocyte is integrally linked to the correct developmental progression of cumulus cell phenotype. In humans and non-human primates, oocyte quality is diminished with in vitro maturation. To determine the changes in gene expression in rhesus monkey cumulus cells (CC) that occur during the final day prior to oocyte maturation and how these changes differ between in vitro and in vivo maturation (IVM and VVM), we completed a detailed comparison of transcriptomes using the Affymetrix gene array. We observe a large number of genes differing in expression when comparing IVM-CC and VVM-CC directly, but a much larger number of differences comparing the transitions from the pre-oocyte maturation to post- IVM and post-VVM state. We observe a truncation or delay in the normal pattern of gene regulation, but also remarkable compensatory changes in gene expression during IVM. Among the genes affected in cumulus cells by IVM are those that contribute to productive cell-cell interactions between cumulus cell and oocyte and between cumulus cells. Numerous genes involved in lipid metabolism are incorrectly regulated during IVM, and the synthesis of sex hormones appears not suppressed during IVM. We identify a panel of 24 marker genes, the expression of which should provide the foundation for understanding how IVM can be improved, for monitoring IVM conditions, and for diagnosing oocyte quality.