Impaired information processing speed (IPS) is common in multiple sclerosis (MS). As a measure of IPS the Paced Auditory Serial Addition Test (PASAT), the measure recommended for serial assessments by the National MS Society Task Force, is influenced by practice effects. Within session practice effects for the PASAT were examined in a sample of 30 individuals with MS. Significant practice effects on all PASAT trials were identified, with the exception of the slowest trial. Those with relapsing-remitting MS showed greater improvement on repeated assessment than those with chronic-progressive MS, on all except the slowest PASAT trial. It was concluded that, due to the extensive practice effects found at faster presentation, serial use of the PASAT in MS samples should either rely on use of slower presentations, or include some correction to account for practice effects.