We focused on the miRNAs that were differentially expressed between azoospermia as a result of an obstruction in the genital tract (i.e. having conserved spermatogenesis) and azoospermia caused by spermatogenic failure, and described, in a miRNA validation stage of the study, the expression values of one miRNA (miR-31-5p) in exosomes from semen as a predictive biomarker test for the origin of azoospermia with high sensitivity and specificity (>90%).