Improvements in using retrieved testicular spermatozoa in infertile males to achieve fertilization and pregnancy has enabled patients with clinical azoospermia and non-obstructive testicular failure to father children. In this review article, we compare the relative yields of the two major techniques for sperm retrieval in males with non-obstructive azoospermia; TESE (Testicular Sperm Extraction) and TESA (Testicular Sperm Aspiration). We also discuss the role of follicle-stimulating hormone (FSH), testicular volume, serum levels of inhibin B, testicular doppler flow pattern, chromosome Yq deletions, and presence of spermatids in azoospermic ejaculates as predictors of presence or absence of spermatozoa in biopsied testicular tissues. In conclusion, although most studies favor the more invasive TESE in terms of sperm retrieval success rate, the degree of certainty in this regard remains unsatisfactory, and future studies need to address the issues of standard error and differential misclassification attributable to needle gauge size in patients undergoing TESA.