This study evaluated whether microsurgical varico-celectomy performed in infertile men with severe oligozoospermia (SO) resulted in improved semen parameters or increased rates of spontaneous pregnancy (SP) and performed a cost-effectiveness analysis comparing intrauterine insemination (IUI), in vitro fertilization (IVF), and varicocelectomy. This study included 25 patients with SO who underwent microsurgical varicocelectomy between September 2019 and May 2022, which resulted in post-surgical SP in all cases. Men with azoospermia, abnormal karyotype, or Y-chromosome microdeletion were excluded from the study. Serum luteinizing, follicle-stimulating, and testosterone hormones were measured preoperatively. Semen was analyzed every 3 months postoperation. The incidence of SP was recorded at each visit. Cost-effectiveness for assisted reproductive technologies was calculated based on reported costs. Several parameters were evaluated as potential predictors of the response to microsurgical varicocelectomy using univariate and multivariate analyses. After a mean postoperative observation period of 7 months, 25 couples with SP after microsurgical varicocelectomy were recruited. The mean sperm concentration increased from 3 million/mL (interquartile range [IQR]: 2-5 million/mL) to 12 million/mL (IQR: 5-17 million/mL; p<0.05), and mean sperm motility improved from 4% (IQR: 3%-6%) to 7.6% (p<0.05). Total motile sperm count (TMSC) increased to 3.08 million (IQR: 1.02-5.83 million) from a preoperative value of 0.34 million (IQR: 0.16-0.83 million). A cost-effectiveness analysis comparing IVF with varicocelectomy indicates that varicocelectomy may represent a better first-line option for infertile men with very low preoperative TMSC. However, further research remains necessary to confirm this result. Varicocelectomy should be discussed as a treatment option for men with SO and may improve sperm quality and fertility potential, resulting in SP.