Purpose: Objective functional tests like the five-repetition sit-to-stand test (5R-STS) can supplement an objective dimension to conventional patient-reported outcome measures. The reliability of unsupervised obtainment of 5R-STS performance is currently unknown. Methods: We included patients with degenerative pathologies of the lumbar spine. Patients performed the 5R-STS during the initial clinical visit (supervised), as well as at home after instruction by a physiotherapist. At home, patients were first timed by a relative (unsupervised) and subsequently produced a video recording of themselves performing the 5R-STS for digital measurement (telesupervised). Two raters independently assessed the recordings. Results: One hundred and twenty-one patients were recruited, of which 100 were eligible. Eighty-eight reported unsupervised results. Sixty-four returned recordings, of which 61 were ratable. Both unsupervised (r: 0.94, 95% CI 0.91–0.96, p < 0.001) and telesupervised (r: 0.90, 95% CI 0.83–0.94, p < 0.001) measurements demonstrated excellent correlation with clinical test times. Patients did not perform more slowly at home (p > 0.05). The interrater agreement for digital judgement of the telesupervised recording was excellent (ICC: 0.996, 95% CI 0.993–0.998, p < 0.001). We confirmed convergent validity with self-reported disability, back pain, and quality of life (all p < 0.05), but not with leg pain (p = 0.189). Conclusions: Unsupervised at-home assessment using the 5R-STS is highly reliable. There does not appear to be a specific need for patients to return for a supervised 5R-STS follow-up. Rather, instructions can be provided, and the test performed and rated by a partner or family member at home. This is logistically and economically advantageous for patients, clinicians, and researchers. Trial registry number: ClinicalTrials.gov Identifier: NCT03321357. Graphical abstract: These slides can be retrieved under Electronic Supplementary Material.[Figure not available: see fulltext.].