Follicle-stimulating hormone (FSH) is a therapeutic option in patients with idiopathic oligozoospermia and normal FSH serum levels. However, few studies have evaluated which dose of FSH is more effective. The aim of this study was to compare the clinical efficacy of the two most frequently used FSH treatment regimens: 75 IU daily vs. 150 IU three times a week. Patients were retrospectively assigned to two groups. The first group (n = 24) was prescribed highly purified FSH (hpFSH) 75 IU/daily (Group A), and the second group (n = 24) was prescribed hpFSH 150 IU three times a week (Group B) for three months. Before and after treatment, each patient underwent semen analysis, evaluation of the percentage of DNA-fragmented spermatozoa, assessment of testicular volume (by ultrasonography), and measurement of FSH and total testosterone (TT) serum levels. Treatment with hpFSH significantly improved conventional sperm parameters. In detail, sperm concentration increased significantly after treatment only in Group A, whereas total sperm count, percentage of spermatozoa with progressive motility, normal morphology, or alive improved significantly in both groups. Interestingly, the percentage of sperm DNA fragmentation decreased significantly in both groups after treatment with hpFSH. FSH serum levels were expectably higher at the end of the treatment than before hpFSH was administered to both groups. Remarkably, TT serum levels only increased significantly in Group A. Finally, testicular volume was significantly higher in Group A after treatment, while it did not change significantly compared to baseline in Group B. The percentage of FSH responders did not differ significantly between the two groups (8/24 vs. 6/24). The daily administration of hpFSH 75 IU seems more effective than using 150 IU three times a week. However, this therapeutic scheme implies a higher number of injections and slightly higher costs.