This article describes the effects of sulfasalazine (SSZ) treatment on serum immunoglobulin (Ig) levels in 6 children with oligoarticular- or polyarticular onset juvenile chronic arthritis (JCA). None of the children who developed dysimmunoglobulinemia during treatment showed clinical symptoms of this adverse event, in particular none developed severe infections. All patients regained normal immunoglobulin levels after discontinuing SSZ treatment. One patient with a partial IgA deficiency at the start of SSZ treatment showed a slow increase in the IgA level during treatment. During follow-up (4-6 years), one patient spontaneously developed a dysimmunoglobulinemia and one patient developed diabetes mellitus. Based on these case reports and review of the literature we advocate monitoring of serum immunoglobulin levels while on SSZ treatment.