 During the first meiotic division in spermatogenesis there are two critical events. First, synapsis between homologous chromosomes and formation of the synaptonemal complex SC, which regulates sister chromatid cohesion and provides the template for localization of recombination machinery proteins. Secondly, recombination between homologous chromosomes, which is essential for the correct segregation. Errors during these two processes may induce incorrect segregation of chromosomes and are a major cause of gamete aneuploidy. The aim of this study was to assess meiotic recombination in primary spermatocytes, synaptonemal complex length and the correlation with chromosomal abnormalities in testicular spermatozoa from infertile men with idiopathic non-obstructive azoospermia NOA. Prospective cohort study to assess meiotic progression, total length of SC, frequency of recombination and sperm aneuploidy in samples obtained from testicular biopsies from NOA patients. The study group was compared with a control group from post-vasectomized OA patients. Immunocytogenetics with SCYP3, CREST and MLH1 antibodies for meiotic progression, SC length, and recombination. Fluorescence in situ Hybridization FISH for chromosomes 1, 4, 6, 13, 16, 18, 21, 22 in primary spermatocytes and chromosomes 13, 18, 21, X, Y on sperm. MicroMeasure 3.3 program was used for SC length. 