Background: Childhood acute lymphoblastic leukemia (ALL) treatment requires numerous lumbar punctures (LPs) with intrathecal (IT) chemotherapy to prevent and treat central nervous system disease. Historically, LPs in this setting are performed using propofol sedation. At our institution, LPs are often alternatively performed under nitrous oxide (N2O). To date, there have been no large scale assessments comparing these sedation methods for this purpose. Procedures: Retrospective cohort study of patients aged 0-31 years with ALL treated between 1/1/2013-12/31/2018 at the Children’s Minnesota Cancer and Blood Disorders Center, including all therapeutic LPs performed in the clinic setting under either propofol or N2O. Results: Among 215 patients and 2677 therapeutic LPs, 56.6% (n = 1515) occurred under N2O with 43.3% (n = 93) of patients using exclusively N2O with all LPs. The incidence of traumatic LPs (RBC ≥ 10 cells/µL) were similar between both treatments (27.3% vs 30.2). Successful IT chemotherapy delivery (99.7% N2O vs 99.8% propofol) did not differ between sedation types. Experiencing a traumatic LP under N2O was associated with a sedation switch for the subsequent LP (aOR 2.40, p=0.002) while older age (aOR 1.08, p<0.0001) and higher BMI percentile (aOR 1.01, p=0.009) were associated with increased likelihood for undergoing a traumatic LP. Conclusion: N2O is an effective sedation option for therapeutic LPs in children with ALL with noninferiority to propofol in terms of IT chemotherapy administration and traumatic LP incidence. For many patients, N2O can effectively replace propofol during LP procedures, which has important safety and quality-of-life implications.