Background: Burnout is known to be high amongst physician trainees. Factors such as stress, fatigue, social environment, and resilience could affect burnout. Cross-sectional data describe burnout in pediatric residents, but the trajectory of burnout in a cohort of residents followed longitudinally through the full course of residency training has not been reported. We prospectively examined the prevalence and trajectory of burnout, stress, fatigue, social connectedness, and resilience in a pediatric resident cohort from orientation through three years of residency. The cohort (N = 33) was surveyed six times between 2015-2018 using the Abbreviated Maslach Burnout Inventory (AMBI), Perceived Stress Scale (PSS), Epworth Sleepiness Scale (ESS), Social Connectedness Scale-Revised (SCS-R), and Connor-Davidson Resilience Scale (CD-RISC10). Data were analyzed using repeated measures mixed effects models. Significant change from baseline was considered to be adjusted p < 0.05. Response rate was >50% at each timepoint; 69% of trainees completed surveys â„4 times. Scores were significantly worse than baseline in all surveys, at every timepoint, with the exception of AMBI-PA (personal accomplishment) at the PGY1/PGY2 transition and SCS-R and CD-RISC10 at the end of training. The most significant changes from baseline occurred mid-PGY1 to mid-PGY2. At least 65% of residents demonstrated worse scores than baseline on 36/ 40 (90%) follow-up surveys. Furthermore, â„65% met criteria for emotional exhaustion and moderate stress at every timepoint. SCS-R was the only survey measure to improve at residency completion compared to baseline. Conclusion: Within 6 months of starting residency this pediatric resident cohort became burned out, stressed, fatigued, less socially connected, and less resilient. Burnout is only one factor that indicates impaired resident well-being. To fully address this, a comprehensive examination of how residents are trained is needed to identify effective interventions.