Colorectal cancer in young patients is often diagnosed late, at advanced stages. These patients have more resistant and aggressive disease, despite similar clinical treatment patterns compared with those with late-onset disease. Background: Compared with the general population, the incidence of young-onset (YO) colorectal cancer (CRC) is increasing. However, a significant knowledge gap exists in the clinical characteristics, treatment patterns, and outcomes for these patients. Materials and Methods: Six international tertiary cancer centers conducted a retrospective study. Patients with YO CRC (aged 18-44 years) and LO CRC (aged > 44 years) diagnosed with histologically proven colorectal adenocarcinoma from June 2003 to June 2014 were enrolled. Patients were randomly chosen from each center's database, and the patient demographics and treatment information were collected. The data were then centralized, and the final analysis was performed at a single institution. Cox proportional hazards models were used to estimate the crude and adjusted hazard ratios (HRs) with 95% confidence intervals (CIs) for progression-free survival and mortality, and YO was compared with LO. Site-specific HRs were pooled using a random-effects meta-analysis. Results: Overall, 498 patients, including 224 with YO (129 men; mean age, 37 +/- 5.5 years) and 274 with LO (167 men; mean age, 64.8 +/- 9.5 years) CRC, were included. At the diagnosis, 137 patients (61.2%) and 122 patients (44.5%) with YO and LO CRC had metastatic disease, respectively. For both cohorts, the 3 most common presenting symptoms were pain, hematochezia, and weight loss. Surgery was performed in 141 YO (63.0%) and 219 LO (79.9%) patients. The longitudinal noncurative treatment patterns were similar, but more biologic therapy was used for these YO patients. The pooled progression-free survival analysis results for first-line noncurative treatment favored LO (HR, 1.96; 95% CI, 1.04-3.68). The mortality analysis showed no significant differences between the 2 groups (YO: HR, 1.53; 95% CI, 0.91-2.58). Conclusion: Despite similar treatment patterns and survival outcomes, YO disease might be clinically more aggressive. (C) 2017 Elsevier Inc. All rights reserved.