Objective: To determine the association between adverse maternal/perinatal outcomes and Canadian and U.S. preeclampsia severity criteria. Methods: Using PIERS data (Preeclampsia Integrated Estimate of RiSk), an international continuous quality improvement project for women hospitalized with preeclampsia, we examined the association between preeclampsia severity criteria and adverse maternal and perinatal outcomes (univariable analysis, Fisher's exact test). Not evaluated were variables performed in <80% of pregnancies (e.g., 24-hour proteinuria). Results: Few of the evaluated variables were associated with adverse maternal (chest pain/dyspnea, thrombocytopenia, ‘elevated liver enzymes’, HELLP syndrome, and creatinine >110 μM) or perinatal outcomes (dBP >110 mm Hg and suspected abruption) (at p < 0.01). Conclusions: In the PIERS cohort, most factors used in the Canadian or American classifications of severe preeclampsia do not predict adverse maternal and/or perinatal outcomes. Future classification systems should take this into account.