Objective: To assess whether men diagnosed with prostate cancer at younger ages have a poorer prognosis. The influence of select factors (race, marital status, stage, histological grade, histology, presence of comorbid cancer, and time of diagnosis) on the relation between age at diagnosis and survival was considered. Methods: Analyses were based on 289,809 men diagnosed with malignant prostate cancer, ages 40 years and older in the Surveillance, Epidemiology, and End Results (SEER) program between 1973 and 1997, actively followed for vital status through 31 December 1998. Cases diagnosed through autopsy or death certificate were excluded. Five-year relative survival and Cox proportional hazards were used for assessment. Results: Five-year relative survival increased, leveled off, and then decreased over the age span. This pattern was most pronounced in men with advanced stage and poor grade tumors. Conditional death hazards that showed significantly higher hazard ratios in younger age groups (i.e. 40–44 and 45–49) represented local/regional stage and poorly differentiated/undifferentiated tumors, distant stage and moderately differentiated, poorly differentiated/undifferentiated, or unknown grade; and unknown stage and unknown grade. The influence of young age on prostate cancer prognosis for advanced stage and poorly differentiated/undifferentiated cases was not significantly influenced by year of diagnosis or race. Conclusions: Younger age is a prognostic factor for prostate cancer survival. The relationship between young age at diagnosis and survival is significantly influenced by stage and histological grade at diagnosis.