ABSTRACT Purpose: To investigate whether renal modifications occur following treatment with dutasteride or finasteride. Methods: Twenty-four male rats were divided into three groups: control (that received distilled water), dutasteride (0.5 mg/kg/day), and finasteride (5 mg/kg/day) groups. All administrations were given by gavage for 40 consecutive days. After inducing euthanasia, blood was collected for urea and creatinine analyses, and both the kidneys were collected for stereological analyses of kidney morphology. Results: Serum urea and creatinine levels were increased in both the finasteride and the dutasteride groups compared with those in the control group. In addition, kidney weight, kidney volume, cortical volume, glomerular volumetric density, and mean glomerular volume were reduced in both treatment groups. Finally, the number of glomeruli per kidney was reduced by 26.8% in the finasteride group and by 51.6% in the dutasteride group compared with that in the control group. Conclusions: The 5-ARIs finasteride and dutasteride promoted morphological and functional damages in rat kidneys. In addition, rats in the dutasteride group showed more severe renal modifications than those in the finasteride group.