Potentilla erecta, the tormentil, and its rhizome extracts have been known for a long time in traditional medicine as a remedy for the treatment of inflammations, wounds, and gastrointestinal disorders. Tormentil rhizomes have also been used as part of alcoholic beverages in Germany, the Ukraine, and Russia. Acute toxicity of an aqueous P. erecta rhizome extract was evaluated with a single dose administered by the intragastric route to rats and mice in dosages of 2.5 g/kg and 6.8 g/kg of body weight, respectively. Further, a single dose of this extract was applied intraperitoneally to rats and mice in dosages of 3.8 and 14.5 g/kg of body weight, respectively. After an observation period of 2 weeks after intragastric administration and 3 days following intraperitoneal administration, no mortality or any changes in appearance, behavior, or body weight occurred for both rats and mice in the high dosages mentioned. Macroscopic and microscopic studies of the internal organs of these rodents revealed no pathological changes. The data are in line with the long-time traditional use of P. erecta rhizome extracts and results from recent clinical trials in which no signs of any toxic effects have been known after the administration of a P. erecta rhizome extract for the treatment of ulcerative colitis in adults and rotavirus-induced diarrhea in children. Thus P. erecta rhizome extracts should be considered safe with respect to acute toxicity when applied to humans.