Acute toxicity and neurobehavioral effects of the veterinary anthelmintic tetramisole were examined in male albino mice. The 24-h median lethal doses of tetramisole were determined by the up-and-down method in mice after oral, subcutaneous and intraperitoneal administrations, and they were 110, 57 and 34 mg/kg, respectively. The intoxicated mice manifested nervousness, crouching, piloerection and tremor. Subcutaneous injection of tetramisole at 0.5 and 1mg/kg did not significantly affect general locomotor activity of the mice in 5-min open-field activity test or negative geotaxis performance and landing foot splay. However, the 1mg/kg dose of tetramisole significantly increased the stereotyped behavior (grooming, sniffing, biting and licking and head bobbing) of the mice when compared to the control group. Daily treatment of mice with tetramisole at 0.5 and 1mg/kg for six consecutive days did not significantly affect their general locomotor activity in the open-field activity test. Both doses of tetramisole significantly increased stereotyped behavior of the mice on days 3, 5 and 8 in comparison with respective control values. Repeated tetramisole treatments (0.5 and 1mg/kg) also significantly decreased the time needed to complete the negative geotaxis task and reduced landing foot splay. All tetramisole-treated mice showed crouching behavior and were nervous and difficult to handle. The results suggest nervous involvement in the acute toxicity of tetramisole. Stereotyped behavior and changes in the negative geotaxis and landing foot splay are reported for the first time in mice treated with tetramisole.