Background: The elucidation of differences between adult and pediatric-onset primary sclerosing cholangitis (PSC) may inform clinical decision making, and whether results of adult PSC clinical trials can be extrapolated to pediatric subjects. Methods: A single-center retrospective analysis of PSC subjects diagnosed during the epoch 2000–13 was conducted. Demographic, clinical, and laboratory data were compared between PSC subjects diagnosed between 0–18 (pediatric) and 19+ (adult) years of age. An adverse outcome was defined as PSC-related death, liver transplant, or malignancy. Survival without any of these was defined as event-free survival. Results: Analyses of 28 pediatric-diagnosed and 59 adult-diagnosed subjects revealed that incidence of early portal hypertension (PHT; P = 0.2), laboratory parameters of liver disease severity, and fibrosis grade at diagnosis were comparable between adult and pediatric PSC subjects. Adult-diagnosed PSC subjects had higher incidences of adverse outcomes compared to pediatric-diagnosed PSC subjects (P = 0.02). The age group 0–18 years (n = 30) had significantly better event-free survival compared to the age group more than 40 years (n = 25; P = 0.03). The prevalence of PHT in adult PSC subjects was 2.6 that of pediatric PSC subjects. PHT adversely affected outcomes in both adult (P < 0.001) and pediatric (P = 0.01) subjects. Adult PSC subjects were more likely to develop biliary complications (BCs; P = 0.001), ascites (P = 0.004), and variceal bleed (P = 0.03). Adult PSC subjects were more likely to have extra-hepatic co-morbidities (P < 0.001). Adult subjects had a longer follow-up duration compared to pediatric subjects (P = 0.06). Conclusion: Despite having a comparable clinical, laboratory, and histologic biomarkers of liver disease severity at the time of diagnosis, adult PSC subjects had a worse outcome compared to pediatric PSC subjects. Possible reasons for this finding include higher incidence of PHT, BCs, extra-hepatic co-morbidities, and longer duration of follow-up.