In a recent Spanish study, 24 patients (17 children and seven adults) reported nightmares after montelukast. In 18 patients, the nightmares appeared within the first week of treatment. In 21 cases, the nightmares rapidly resolved after montelukast had been discontinued (Cereza et al. 2012 ). The relatively high ROR indicates a strong statistical relation between montelukast and nightmares. This was true for both the Dutch and worldwide population. Although nightmares are often transient in children, they can be frightening for both child and parents and can influence school performance. In adults, sleep disorders can lead to potential dangerous situations in traffic or working with machines (Levin and Nielsen 2007 ; Simor et al. 2012 ). This means that the clinician must discuss the possibility of these adverse events with the patient and parents.