Aims and Objectives The self‐performance of a Five‐Times‐Sit‐To‐Stand (FTSTS)‐test, without the usual supervision by a medical professional, provides valuable opportunities for clinical practice and research. This study aimed: (1) to determine the validity of the self‐performed FTSTS test in comparison to a supervised reference test and (2) to determine the reliability of a self‐performed FTSTS test by cancer survivors. Background Early detection of frailty in cancer survivors may enable prehabilitation interventions before surgery or intensive treatment, improving cancer outcomes. Design A repeated measures reliability and agreement study, with one week in between measures, was performed. Methods Cancer survivors (n = 151) performed two FTSTS tests themselves. One additional reference FTSTS test was supervised by a physical therapist. The intraclass correlation coefficient (ICC), structural error of measurement (SEM) and minimally important clinical difference (MID) were calculated comparing a self‐performed FTSTS test to the reference test, and comparing two self‐performed FTSTS tests. The Guidelines for Reporting Reliability and Agreement Studies (GRASS) have been used. Results Mean age of cancer survivors was 65.6 years (SD = 9.3), 54.6% were female, median time since diagnosis was 2 years IQR = 1, and tumour type varied (e.g., breast cancer (31.8%), prostate cancer (17.2%), gastrointestinal cancer (11.9%) and haematological cancer (11.9%)). Validity of the self‐performed FTSTS test at home was acceptable in comparison with the reference test (ICC = .74; SEM = 3.2; MID = 3.6) as was the reliability of the self‐performed FTSTS test (ICC = .70; SEM = 2.2; MID = 3.8). Conclusions The self‐performed FTSTS test is a valid and reliable measure to assess lower body function and has potential to be used as objective (pre‐)screening tool for frailty in cancer survivors. Relevance to clinical practice The self‐performed FTSTS test at home may indicate the cancer survivors in need of prehabilitation in advance of surgery or intensive treatment. The feasibility, short amount of time needed and potential cost‐effectiveness of the self‐performed FTSTS test can make it a valuable contribution to personalised care and precision medicine.