Background according to the revised sarcopenia definition proposed by the European Working Group on Sarcopenia in Older People (EWGSOP2) and revised definition of the Asian Working Group for Sarcopenia (AWGS2019), handgrip strength (HGS) and chair stand test (CST) can be used interchangeably as initial diagnostic measures. Objective to assess the agreement between sarcopenia prevalence, using either HGS or CST, and their association with adverse outcomes in geriatric rehabilitation inpatients. Methods REStORing health of acutely unwell adulTs is an observational, longitudinal cohort of geriatric rehabilitation inpatients. Cohen’s kappa (κ) was used to assess the agreement between sarcopenia prevalence (no, probable and confirmed and severe sarcopenia) according to EWGSOP2 and AWGS2019 using either HGS or CST. Associations between HGS and CST and readmission, institutionalisation and mortality were assessed by binomial regression. Results patients (n = 1,250, 57% females) had a median age of 83.1 years (interquartile range: [77.5–88.3]). There was no agreement between probable sarcopenia prevalence using HGS or CST for EWGSOP2 and AWGS2019, respectively (HGS: 70.9% and 76.2%; CST: 95.5% and 98.4%; κ = 0.08 and 0.02). Agreement between confirmed and severe sarcopenia prevalence using either HGS or CST was strong to almost perfect. HGS was associated with 3-month institutionalisation and 3-month and 1-year mortality, whereas CST was not associated. Conclusions HGS and CST cannot be used interchangeably as diagnostic measures for probable sarcopenia in geriatric rehabilitation inpatients. CST is not useful to predict adverse outcomes in geriatric rehabilitation inpatients.