Several clinical and experimental studies have demonstrated that there are clear sex differences in renal function and disease. Men have a greater risk of developing non-diabetic chronic kidney disease (CKD) and progressing to end-stage renal disease compared to women. However, this sexual dimorphism is not observed in patients with diabetic nephropathy. Experimental studies have shown a role for sex hormones, primarily androgens and estrogens, in the regulation of renal physiology and pathology. While it is generally thought that the beneficial effects of estrogens contribute to the relative protection of women against renal disease, it is also possible that the presence of androgens increases the risk of men to develop CKD. Important modulators of renal function that have been shown to be influenced by sex include the renin-angiotensin system, the sympathetic nervous system, the endothelin system and nitric oxide, and the effects of sex hormones on these systems may be involved in the sex differences observed in progression of CKD. Understanding sex differences in renal function and progression of renal disease is critical for optimal treatment of CKD and understanding differences in the response to renal therapies and improving treatment options for both men and women with renal disease.