<h4>Background</h4>Bladder dysfunction is a common feature of multiple sclerosis (MS).<h4>Objective</h4>In this study we aimed to assess the efficacy, tolerability and safety of Sativex(®) (nabiximols) as an add-on therapy in alleviating bladder symptoms in patients with MS.<h4>Methods</h4>We undertook a 10-week, double-blind, randomized, placebo-controlled, parallel-group trial in 135 randomized subjects with MS and overactive bladder (OAB).<h4>Results</h4>The primary endpoint was the reduction in daily number of urinary incontinence episodes from baseline to end of treatment (8 weeks). Other endpoints included incidence of nocturia and urgency, overall bladder condition (OBC), daytime frequency, Incontinence Quality of Life (I-QOL), Patient's Global Impression of Change (PGIC) and volume voided. The primary endpoint showed little difference between Sativex and placebo. Four out of seven secondary endpoints were significantly in favour of Sativex: number of episodes of nocturia (adjusted mean difference -0.28, p = 0.010), OBC (-1.16, p = 0.001), number of voids/day (-0.85, p = 0.001) and PGIC (p = 0.005). Of the other endpoints, number of daytime voids was statistically significantly in favour of Sativex (-0.57, p = 0.044). The improvement in I-QOL was in favour of Sativex but did not reach statistical significance.<h4>Conclusions</h4>Although the primary endpoint did not reach statistical significance, we conclude that Sativex did have some impact on the symptoms of overactive bladder in patients with MS, providing evidence of some improvement in symptoms associated with bladder dysfunction in these subjects.