The dietary supplement Citicoline free-base (choline cytidine 5'-pyrophosphate) was toxicologically evaluated in Sprague-Dawley rats using oral gavage. In an acute 14-day study, 2000 mg/kg was well tolerated. In a 90-day study, 100, 350, and 1000 mg/kg/day doses resulted in no mortality. In males, slight significant increases in serum creatinine (350 and 1000 mg/kg/day), and decreases in urine volume (all treated groups) were observed. In females, slight significant increases in total white blood cell and absolute lymphocyte counts (1000 mg/kg/day), and blood urea nitrogen (BUN) (100 and 350, but not 1000 mg/kg/day) were noted. A dose-related increase in renal tubular mineralization, without degenerative or inflammatory reaction, was found in females (all treated groups) and two males (1000 mg/kg/day). Renal mineralization in rats (especially females) is influenced by calcium:phosphorus ratios in the diet. A high level of citicoline consumption resulted in increased phosphorus intake in the rats, and likely explains this result.