Background: Deranged serum phosphate (Phos) levels are associated with anemia in hospitalized patients, but their relevance to critical illness is unclear. Therefore, our goal was to investigate whether abnormal Phos on admission to the surgical intensive care unit (ICU) is associated with anemia. Materials and Methods: We performed a retrospective analysis of data from an ongoing study of nutrition in critical illness. Serum Phos and hemoglobin levels were obtained at ICU admission. Normal Phos was defined as 2.5–4.0 mg/dL. To investigate the association between Phos and anemia, we performed logistic regression analyses, while controlling for age, sex, race, body mass index, Nutrition Risk Screening score, Deyo-Charlson Comorbidity Index, creatinine, mean corpuscular volume, and serum albumin. Results: In total, 510 patients comprised the analytic cohort; 62% were anemic, 30% had Phos >4.0 mg/dL, and 14% had levels <2.5 mg/dL. Logistic regression analysis demonstrated each unit increment in Phos was associated with a 25% higher likelihood of anemia (odds ratio [OR], 1.25; 95% confidence interval [CI], 1.04–1.50). Moreover, patients with Phos >4.0 mg/dL had a 68% higher likelihood of anemia compared with those with normal levels (OR, 1.68; 95% CI, 1.02–2.80). Patients with Phos <2.5 mg/dL were not more likely to be anemic compared with those with normal levels. Conclusion: Surgical ICU patients with admission Phos >4.0 mg/dL are more likely to be anemic compared with those with normal levels. Our findings support the need for studies to determine whether globally maintaining optimal Phos reduces the likelihood of anemia and whether ideal Phos during acute care hospitalization influences clinical outcomes.