Background: Patients admitted to the hospital on weekends experience worse outcomes than those admitted on weekdays. Patients with cancer may be especially vulnerable to the effects of weekend care. Our objective was to compare the care and outcomes of patients with cancer admitted urgently to the hospital on weekends and holidays versus those of patients with cancer admitted at other times. Materials and Methods: This was a retrospective study of all adult patients with cancer having an urgent hospitalization in Canada from 2010 to 2013. Patients admitted to hospital on weekends/holidays were compared with those admitted on weekdays. The primary outcome was 7-day in-hospital mortality. We also compared performance of procedures in the first 2 days of hospital admission and admission to critical care after the first 24 hours. Results: 290,471 hospital admissions were included. Patients admitted to hospital on weekends/holidays had an increased risk of 7-day in-hospital mortality (4.8% vs 4.3%; adjusted odds ratio [OR], 1.13; 95% CI, 1.08–1.17), corresponding to 137 excess deaths per year compared with the weekday group. This risk persisted after restricting the analysis to patients arriving by ambulance (7.1% vs 6.4%; adjusted OR, 1.11; 95% CI, 1.04–1.18). Among those who had procedures in the first 4 days of admission, fewer weekend/holiday-admitted patients had them performed in the first 2 days, for 8 of 9 common procedure groups. There was no difference in critical care admission risk after the first 24 hours. Conclusions: Patients with cancer admitted to the hospital on weekends/holidays experience higher mortality relative to patients admitted on weekdays. This may result from different care processes for weekend/holiday patients, including delayed procedures. Future research is needed to identify key outcome-driving procedures, and ensure timely access to these on all days of the week.