AbstractBackgroundAltered trace element status is associated with epilepsy in humans and dogs with idiopathic epilepsy (IE).ObjectivesCompare hair element concentrations in epileptic and healthy dogs.AnimalsSixty‐three dogs with IE (53 treated, 10 untreated) and 42 controls.MethodsCase‐control study using ICP‐MS to determine hair calcium, magnesium, phosphorus, sodium, potassium, iron, copper, manganese, zinc, selenium, chromium, lead, mercury, cadmium, arsenic, aluminum, and nickel concentration. Groups were compared using nonparametric tests. Results were controlled for diet, sex, age, and hair color using generalized linear mixed models.ResultsCompared to healthy controls, dogs with IE had lower hair phosphorus (mean ± SD; IE: 286.19 ± 69.62 μg/g, healthy: 324.52 ± 58.69 μg/g;P= .001), higher hair copper (IE: 10.97 ± 3.51 μg/g, healthy: 8.41 ± 1.27 μg/g;P< .001), zinc (IE: 158.25 ± 19.64 μg/g, healthy: 144.76 ± 32.18 μg/g;P< .001), copper/zinc ratio (IE: 0.07 ± 0.02, healthy: 0.06 ± 0.01;P= .003), selenium (IE: 1.65 ± 0.43 μg/g, healthy: 0.94 ± 0.73 μg/g;P< .001), and arsenic (IE: 0.40 ± 0.78 μg/g, healthy: 0.05 ± 0.08 μg/g;P< .001). When comparing treated and untreated epileptic dogs with healthy dogs, the differences in phosphorus and selenium remained significant for both groups, whereas the differences in copper, zinc, and arsenic were significant only for treated dogs. Potassium bromide treatment was strongly associated with high hair arsenic (P= .000).Conclusions and Clinical ImportanceAltered trace element status could be involved in the pathophysiology of IE in dogs. Antiseizure drugs might affect trace element and arsenic metabolism.