A number of medications commonly used in pediatric psychopharmacology can prolong the QTc interval of the electrocardiogram. QTc prolongation can in turn predispose to torsades de pointes, a sometimes deadly arrhythmia. These considerations are clinically relevant given documented, if still controversial, reports of sudden deaths associated with the use of the tricyclic antidepressant (TCA) desipramine in children. While most reports of QTc prolongation have involved adult patients, this adverse effect can occur in children. After discussing the QTc parameter's derivation, accuracy, and limitations, this article reviews current knowledge about the propensity of the antipsychotics (both atypical and traditional), TCAs, and alpha agonists to prolong the QTc interval in young patients. Based on the literature reviewed, guidelines are provided for clinical and electrocardiographic monitoring in pediatric psychopharmacology.