The Strength, Assistance for walking, Rise from a chair, Climb stairs and Falls (SARC-F) score is a tool recommended for screening the risk of sarcopenia in older patients. However, the association between SARC-F or SARC-F + calf circumference (SARC-F + CC) and the Charlson Comorbidity Index (CCI) in hospitalized older cancer patients is not fully understood. Thus, our aim is to evaluate the association between the SARC-F or SARC-F + CC and the presence of comorbidities and risk of death in older hospitalized cancer patients. A cross-sectional study involving 90 (42 M/48F) hospitalized cancer patients over 60 years old with ongoing chemotherapy or surgical treatment is carried out. The SARC-F is performed to assess the muscle function loss (MFL if SARC-F ≥ 4), sarcopenia (SARC-F ≥ 6) and sarcopenia using the calf circumference (SARC-F + CC ≥11). CC is assessed using an inelastic tape. The CCI is used to assess the presence of comorbidities. Logistic regression is used to evaluate the association between the SARC-F and Charlson Comorbidity Index. Mean of age is 67.8 years and half (49%) of the patients present MFL (SARC-F ≥ 4), 31% present sarcopenia using the SARC-F ≥ 6 and 60% using the SARC-F + calf circumference ≥ 11. Although no association in the crude model, there is association after adjusting by age, sex, alcohol use, smoking habit, physical activity, use of oral nutritional supplementation, body mass index, performance status, tumor, and treatment type between SARC-F ≥ 4 or ≥ 6 and CCI (SARC-F ≥ 4 × CCI: OR: 2.31 [95%CI: 1.02–5.23], p = 0.04) and (SARC-F ≥ 6 × CCI: OR: 3.24 [95%CI: 1.21–8.65], p = 0.01), respectively. However, this association is lost when using the SARC-F + calf circumference (SARC-F + CC ≥11 × CCI: OR: 1.12 [95%CI: 0.63–1.90], p = 0.68). In conclusion, screening for the risk of sarcopenia in older cancer patients is highly recommended as sarcopenia is tightly associated with the clinical outcome. The use of the SARC-F score using a cut-off ≥4 or ≥ 6 is more relevant for clinical practice to detect comorbidities and risk of death than the use of SARC-F with the calf circumference.