A Canadian cohort study showed that the risk of severe neonatal morbidity or mortality increases with the number of maternal chronic diseases. The study included more than 1 million births. The risk increased gradually with the number of preexisting chronic conditions of the mother. Neonatal mortality increased with the number of maternal chronic conditions. Data were adjusted between factors for a more accurate impact assessment. The main finding confirms the dose effect of maternal chronic diseases on neonatal outcomes.