- Objective The aim of this study was to evaluate the association between maternal smoking during pregnancy and future risk of childhood neoplasm risk. Study design A population based cohort analysis comparing the risk for long-term childhood neoplasms in children born (1991–2014) to mothers that smoked during pregnancy vs. those that did not. Childhood neoplasms were pre-defined based on ICD-9 codes, as recorded in the hospital medical files. Children with congenital malformations and multiple gestations were excluded from the analysis. Kaplan-Meier survival curves were constructed to compare cumulative oncological morbidity over time. Cox proportional hazards model was used to control for confounders. Results 241,273 infants met the inclusion criteria; out of those 2841 were born to mothers that smoked during pregnancy. Offspring to smoking mothers had higher incidence of benign (OR 1.6, 95%CI 1.02–2.58; p value = .038) but not malignant tumors. Total cumulative neoplasm incidence was significantly higher in smoking women (Log Rank = 0.001) but no significant difference in the incidence of malignant tumors was noted (Log Rank = 0.834). In a Cox regression model controlling for maternal confounders; a history of maternal smoking during pregnancy remained independently associated only with increased risk for benign tumors (adjusted HR 2.5, 95%CI 1.57–3.83, p = .001). Conclusion Maternal smoking during pregnancy is associated with increased long-term risk for benign but not malignant tumors. This is important when counseling mothers regarding potential future risks and recommended lifestyle modifications. Despite this large population study with long follow-up, childhood malignancies are rare, and clarifying the possible association may require further studies.