BackgroundLong-term results and factors affecting outcomes of vacuum bell therapy for pectus excavatum are relatively unknown. MethodsWe conducted a retrospective study on patients (<18y) treated with vacuum bell therapy between May 2008 and October 2021. Primary outcome was treatment success; secondary outcomes were analysis of daily time spent on treatment, treatment duration, complications, long-term follow-up, treatment for patients awaiting a Nuss procedure, treatment for female patients, and factors affecting outcomes. ResultsOf 259 patients treated with vacuum bell therapy, 18.9% (n=49/259) were still being treated, 17.4% (n=45/259) were lost to follow-up and 63.7% (n=165/259) completed treatment, with a 52.1% (n=86/165) success rate . Median follow-up was 64.0 months (interquartile range 48.0-87.0). More time spent daily on vacuum bell therapy, total treatment duration, and overnight use led to a higher success rate (P=.002, P<.001, P<.001 resp.). Complications (22.8%, n=59/259) were minor, recurrence occurred in 2.3% (n=2/86) of patients. Of the patients treated while awaiting a Nuss procedure, 26.7% (n=4/15) no longer required the Nuss procedure. Breast growth made 39.3% (n=11/28) of female patients quit treatment. Deeper deformities (P=.02, P=.009), flexible chest wall (P=.007) and symptomatic pectus excavatum (P=.02) resulted in lower success rates. ConclusionsVacuum bell therapy is successful in up to 52.1% of patients. Overnight vacuum bell use and treatment while awaiting a Nuss procedure should be encouraged. Older patients with a stiff chest wall can be successfully treated with prolonged treatment. For female patients watchful waiting or early treatment, to prevent challenges during breast growth, is preferred. Level of evidenceLevel II