Intrathecal baclofen (ITB) application has become the first choice in the management of otherwise intractable generalized spasticity. The mechanism whereby ITB alleviates increased skeletal muscle tone is generally accepted; however, less is known about its effect on smooth muscles. The authors present two patients who developed a paralytic ileus during ITB infusion for supraspinal spasticity. In addition, they performed a retrospective chart analysis of another 12 patients receiving ITB with respect to their intestinal function. They calculated the cumulative sum of days without bowel movements plus the cumulative sum of interventions intended to promote intestinal peristalsis before and during ITB treatment. Intestinal function deteriorated in 10, remained unchanged in one, and improved in three patients compared to baseline, irrespective of concomitant oral baclofen medication. This is the first study addressing a previously unnoticed, but potentially deleterious side effect of ITB treatment. The findings suggest, however, that close observation of intestinal activity in conjunction with the generous use of prokinetic, laxantic or eubiotic drugs may allow for continuation of ITB treatment, even in particularly sensitive patients.