Glutethimide has been used to control essential tremor. Its efficacy in the treatment of disabling cerebellar and rubral tremor was assessed in an open study of six patients with multiple sclerosis and two patients with traumatic brain injury. Functional and quantitative tremor severity was assessed before treatment and 7 to 14 days after a stable dose was achieved. Six of eight patients exhibited visible functional benefit from treatment with glutethimide; abstract testing results correlated well with functional status in most cases. Four patients chose to continue to receive medication. Controlled trials of glutethimide to compare its efficacy with that of other medications used in the treatment of action tremor are indicated.