Purpose The efficacy of traditional Mehta casting in the treatment of early onset scoliosis (EOS) is well-established. However, waterproof casting has not been previously described. Inherent advantages of waterproof casting include clearance for bathing/swimming, avoiding cast holidays, and improved family satisfaction. The purpose of this study was to assess the safety and efficacy of waterproof serial casting at controlling curve progression in EOS. Methods The current study is an IRB-approved Level IV retrospective consecutive cohort of EOS patients who underwent a serial 75% body weight traction-elongation-flexion Mehta cast protocol with waterproof cast padding. The addition of 3-point apical translation with stockinettes was utilized during casting. Bracing was initiated after correction < 15 degrees or 1 year of serial casting. Results Seventeen patients at mean age 21.6 months, with pre-cast Cobb angle 52.3 degrees (R: 35 degrees-82 degrees), underwent serial waterproof casting. In-cast correction index was 64%; for post-cast, Cobb angle was 18.6 degrees. At mean 5.6 years follow-up (R: 2.3-8.9 years), 82% successfully avoided surgical intervention, 53% maintained correction < 25 degrees, and 29% are considered "cured". 3/17 (18%) underwent a 2nd round of casting, and a total of 3/17 (18%) ultimately required surgery at 6.2 years post-casting. No major cast-related complications, decubiti, or cast holidays were encountered. Conclusion Serial waterproof casting is safe and efficacious in EOS when compared to published results of traditional Mehta casting. Of 17 patients with mean pre-cast Cobb 52.3 degrees, 82% successfully avoided surgery and 53% maintained mild curves < 25 degrees magnitude at 5.6 years follow-up. No major complications or skin decubiti occurred, and advantages include clearance for bathing and avoidance of need for cast holidays during treatment.