Objectives To prospectively assess, using polysomnography (PSG), the evolution in obstructive sleep apnea (OSA) in infants with Robin Sequence (RS) during their first year of life and to evaluate the role of PSG in OSA treatment. Methods Prospective and longitudinal study conducted in 2 tertiary hospitals (2018-2021). Data from 2 PSG (PSG1 0-3 months of life, PSG2 6-10 months of life) performed in RS infants in different sleep positions/conditions (without treatment: supine [SP]; with treatment: lateral [LP], prone [PP], respiratory support) were analyzed. OSA treatment type were compared before and after both PSG. Results Among the 45 RS infants included (median [IQR] age 2[1-2] months at PSG1 and 8[6-8] months at PSG2), 27 had available data from both PSG1/PSG2. Sleep efficacy without treatment (SP) tended to be lower at PSG1 than PSG2 (77%[66-84] versus 88%[78-96], p=0.0048). At PSG1 without treatment, 77% of infants had a severe OSA; OAHI significantly decreased between PSG1 and PSG2 (17/h[10-36 versus 5/h[3-7], p<0.0001). At PSG1 under treatment, despite an improvement in OAHI, OSA remained severe for 81% of infants in LP, 47% in PP, and 85% with respiratory support (16/h[11-21],10/h[6-17],18/h[11-20], respectively). PSG1 led to a change in treatment for 40% of infants (de-escalation 18%; escalation 22%). Conclusion Sleep and OSA improved spontaneously during the first months of life in RS infants, approaching near-normal at 8 months of age. Early PSG led to a change in management strategy in nearly half the RS infants, highlighting that PSG represents a precious tool to optimize OSA treatment.