Objective Vallecular cyst coexisting with laryngomalacia (VC‐LM) can cause significant pharyngolaryngeal obstruction. Traditionally, it is diagnosed with flexible endoscopy (FE) and treated by rigid endoscopy. This study evaluates the effectiveness of solely using FE with novel noninvasive ventilation (NIV) of sustained pharyngeal inflation (SPI) support for both diagnosis and treatment in such infants. Methods A retrospective review of consecutive infants who were diagnosed and treated for VC‐LM in the 12‐year period, 2007 to 2018, was conducted. Clinical variables, techniques, and outcomes were analyzed and reported. Results Eighteen infants (10 males) were included. The mean age was 3.0 ± 0.6 months and the mean body weight was 4.6 ± 1.3 kg. Before FE, 14 infants were supported with bi‐nasal prongs NIV (BN‐NIV) and four infants with tracheal intubation. During diagnostic and therapeutic FE, all infants supported with a nasopharyngeal NIV (NP‐NIV) only. All diagnoses were made in the first FE inspection of 3.5 ± 1.2 minutes. Thirteen lesions were immediately treated with FE laser therapy in 18.1 ± 1.7 minutes in the same FE course. Total FE time was 24.6 ± 2.8 minutes. Three infants needed revision laser therapy 4 days later. There was no desaturation (<90%), bradycardia (<100/min), or pneumothorax. After FE therapy, all infants were supported with BN‐NIV only with significantly (<0.01) lower pressure and completely weaned off before being discharged 8.4 ± 1.5 days later. All infants, followed up for a 6‐month period, showed many clinical improvements. Conclusions FE, with this NP‐NIV and SPI supports, could offer accurate diagnosis and successful laser therapy of the VC‐LM with procedural sedation in the same session in infants.