Therapy with disease modifying antirheumatic agents (DMARDs) is often complicated by the occurrence of adverse effects. Although risk factors for several DMARDs have been reported, the prediction of adverse drug reactions is not yet possible. Therefore regular monitoring remains mandatory. Monitoring for adverse effects to DMARDs usually includes one or more of the following: blood count, liver, kidney, urine or ophthalmologic tests. Since most adverse reactions occur during the first few months of treatment, monitoring should be more intense and frequent in this initial phase. Some adverse effects are dose-dependent, and therefore dosage reduction may help alleviate these. Others are idiosyncratic, and often necessitate drug withdrawal. Except for (hydroxy)chloroquine-induced retinopathy and methotrexate-induced liver cirrhosis, most adverse reactions to DMARDs are fortunately reversible.