Botulinum toxin (BT) is a neurotoxin that paralyzes muscles by inhibiting release of acetylcholine from presynaptic vesicles at the neuromuscular junction. In people with multiple sclerosis (MS), clinical experience and research studies show that local injection of minute quantities of BT can temporarily control skeletal muscle spasticity, bladder detrusor hyperreflexia, and tremor. Specifically, BT injections have been shown to reduce muscle tone and improve passive function, and possibly improve active function, in patients with spasticity. Injection of BT into the bladder wall is a uniquely effective, safe, and durable treatment in patients with neurogenic detrusor hyperreflexia due to MS who have insufficient response or who do not tolerate oral antimuscarinic medications. This procedure has markedly reduced the need for indwelling catheters and bladder surgery. In addition, a recent study suggests BT may be effective for select patients with MS-associated upper extremity tremor. Appropriate use of BT can improve quality of life for many patients with MS.