[Show abstract][Hide abstract] ABSTRACT: An infertile couple whose female partner showed recurrent retrieval of immature metaphase I (MI) oocytes that were resistant to in-vitro maturation, was studied. Four spermiograms revealed teratozoospermia. Consistent non-fertilization and negative pregnancy outcomes were obtained after intrauterine insemination, gamete intra-Fallopian transfer and IVF. Two intracytoplasmic sperm injection (ICSI) cycles were finally performed. All oocytes (n = 17) in both cycles were arrested at MI and failed to mature after 48 h culture. ICSI also resulted in total non-fertilization. In the last cycle, two oocytes were analysed by transmission electron microscopy and showed almost identical results. All organelles showed normal characteristics of an MI oocyte. The main abnormality found was related to the MI spindle, with absence of microtubules and dispersion of the female chromosomes. Minor abnormalities were observed (immature fibrous appearance of the zona pellucida; the presence of small vesicle aggregates which formed a foam-like body). The injected sperm nucleus was arrested in the middle of the chromatin decondensation process, with no visible nuclear envelope reformation. Normal disruption of sperm acrosomal and flagellar components were observed. Only a partial cortical reaction was observed. This represents the first documented case of developmental arrest due to complete absence of spindle formation in association with an otherwise mature ooplasm.