L-carnitine (LC) deficiency is commonly observed in chronic hemodialysis (HD) patients. As a result of this and other causes of secondary LC deficiencies, LC has been described as a "conditionally essential nutrient" or "conditional vitamin". Although a large number of clinical trials regarding the beneficial effects of LC administration in HD patients have been published, some controversy about its use in this indication persists. In this article, we will review the use of LC in dialysis patients, by focussing mainly on those experimental and clinical data supporting the notion that supra-physiological concentrations of LC in plasma and target organs may exert beneficial effects on several metabolic parameters that have derangements of a common origin (e.g. insulin resistance, type 2 diabetes, dyslipidemia) and which are frequently present in end-stage renal disease (ESRD) patients undergoing dialysis.