Intellectual disability is frequently accompanied by psychiatric symptoms that require pharmacological interventions. Treatment guidelines often provide a general treatment approach for these symptoms in intellectual disability. However, this may not always be the best strategy, as illustrated here in Kleefstra syndrome. We present 3 patients showing severe regression after sleep disturbances. If these are treated with care as usual (eg, behavioral programs and sleep medication) deterioration is likely to follow. It is observed that rapid treatment with relatively high dosages of antipsychotics contributes to restore sleep, halt further regression, and improve daily life functioning.