Long-term exposure to cyanide and/or its main metabolite, thiocyanate, has been associated with goiter, pancreatic diabetes and several neurological disorders. However, very little is found in the literature relating the nephrotoxic and hepatotoxic effects of these substances. Thus, the objective of the present study was to verify the effects of prolonged exposure to potassium cyanide (KCN) in these organs. Forty-six male adults rats, weighing approximately 200 g at the beginning of the experiment, were distributed into five groups-four experimental and one control. Experimental groups were dosed with target doses of 0.3, 0.9, 3.0 or 9.0 mg KCN/kg per day, in the drinking water, during 15 days and the control groups received only tap water. At the end of this experiment, all rats were subjected to euthanasia and plasma samples were obtained in order to determine thiocyanate and thyroidal hormones levels and fragments of thyroid, kidney and liver were collected. Rats treated with the highest cyanide dose (9.0 mg KCN/kg per day) showed lower body weight gain. An increase in the thiocyanate levels was verified in all experimental groups. The histopathologic study revealed hydropic degeneration of the renal tubular epithelial cells in those animals, which received KCN at the dose of 3.0-9.0 mg/kg per day. This study also showed hydropic degeneration of the hepatocytes of those animals, which received KCN at a dose of 9.0 mg/kg per day, and in the thyroid gland an increase was observed in the number of reabsorption vacuoles on follicular colloid, in a dose-dependent manner, in all animals of the experimental groups.