In February 2023, due to the occurrence of deaths among crossbred Afshari-Booroola lambs, a visit was conducted to examine the sick and at-risk animals to investigate the cause of the disease. Clinical examination of the affected animals before death revealed weakness, depression, anorexia, fever, icterus, pale mucous membranes, tachycardia, tachypnea, dyspnea, recumbency, and decreased rumen motility. Some neurological signs such as confusion and tetra paresis were also observed. Blood samples were collected from the jugular vein for hematological and biochemical analyses. Urine samples were also collected for urinalysis. Post-mortem findings in the necropsied and dead animals revealed generalized jaundice (icterus), yellow and friable livers, distended gallbladders with thick and dark bile, and kidneys with a reddish-brown to black color (\\\"metallic kidneys\\\"). Based on the results of hematological, biochemical, and high copper concentrations in the liver, kidneys, and serum of the sick and dead lambs, chronic copper poisoning was identified as the cause of death after ruling out other causes of jaundice syndrome. The source of high copper intake was identified as the use of concentrate formulated for cattle in the lambs\\\' feed and the availability of copper-containing lick stones to the lambs. By limiting copper intake in the lambs\\\' feed, adjusting the copper-to-molybdenum ratio in the diet, and reducing stress factors, the occurrence of new cases of the disease was prevented.

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