Although evidence suggests an inverse association between calcium intake and colorectal cancer incidence, the influence of calcium on survival after colorectal cancer diagnosis remains unclear. We prospectively assessed the association of postdiagnostic calcium intake with colorectal cancer-specific and overall mortality among 1,660 nonmetastatic colorectal cancer patients within the Nurses' Health Study and the Health Professionals Follow-up Study. Patients completed a validated food frequency questionnaire between 6 months and 4 years after diagnosis and were followed up for death. Multivariable hazard ratios (HRs) and 95% confidence intervals (95% CI) were calculated using Cox proportional hazards regression. Comparing the highest with the lowest quartile intake of postdiagnostic total calcium, the multivariable HRs were 0.56 (95% CI, 0.32-0.96; = 0.04) for colorectal cancer-specific mortality and 0.80 (95% CI, 0.59-1.09; = 0.11) for all-cause mortality. Postdiagnostic supplemental calcium intake was also inversely associated with colorectal cancer-specific mortality (HR, 0.67; 95% CI, 0.42-1.06; = 0.047) and all-cause mortality (HR, 0.71; 95% CI, 0.54-0.94; = 0.008), although these inverse associations were primarily observed in women. In addition, calcium from diet or dairy sources was associated with lower risk in men. Higher calcium intake after the diagnosis may be associated with a lower risk of death among patients with colorectal cancer. If confirmed, these findings may provide support for the nutritional recommendations of maintaining sufficient calcium intake among colorectal cancer survivors.