In order to assess the effectiveness of monthly intravenous corticosteroids in reducing childbirth-associated acute exacerbations in multiple sclerosis (MS), we compared pregnant patients followed up in our MS clinic. During the first period (1996-1998), 22 patients did not receive any treatment after delivery. During the second period (1999-2001), following the publication of the PRIMS study, 20 patients were treated monthly with 1 g of intravenous corticosteroids during the six months of the postpartum period. In both groups the relapse rate increased during the first trimester postpartum but it was higher in the untreated group (2+/-0.66 [mean+/-SD]) compared with the treated group (0.8+/-0.41) (P=0.018), suggesting a beneficial effect of monthly intravenous corticosteroids.