PURPOSE: People with painful vertebral degenerative disease are characterized as having difficulty with transitional movements, such as the sit-to-stand movement. A valid and feasible tool is needed to help clinicians quantify the ability of people with painful vertebral degenerative disease to perform transitional movements. Few studies have been conducted to evaluate patients' performance during different phases of sit-to-stand. The purpose of this study was to develop a three-phase sit-to-stand testing (3PSST) instrument for PVDD patients and to investigate the PVDD impacts on the elderly subjects. METHODS: Forty-one elderly subjects(67.1±9.0 years)from an orthopedic clinic with PVDD were examined before the surgery or other treatments. Thirty age-matched community healthy elderly dwellers (72.5±5.4 years) were included in this study as control group volunteers (CG). Sit-to-stand performance tests were conducted using a force plate to measure the ground reaction force (GRF) and center of pressure (COP). Switches mounted on chair back and chair seat were used to separate the whole sit-to-stand course into three phases: (1) reaction time (RT), from start signal (SS) to trunk left chair back (TL), (2) trunk movement time (TMT), from TL to buttock left the chair seat (BL), and (3) stand movement time (SMT), from BL to the maximum GRF (MGRF). MGRF were normalized with individual body weight (BW) before group comparison. RESULTS: The results demonstrated that PVDD group subjects had significant poor sit-to-stand performance than the CG subjects: slower RT (0.89±0.49 vs. 0.70±0.30 sec, P<.05), slower TMT (0.90±0.97 vs. 0.40±0.12 sec, P<.05), and slower SMT (0.40±0.95 vs. 0.10±0.12 sec, P<.05). PVDD subjects also demonstrated significant smaller MGRF than CG (1.20±0.08 vs. 1.29±0.10BW, p< 0.05). CONCLUSIONS: The 3PSST displays validity properties at discriminating between subjects with and subjects without PVDD that make this test potentially useful in clinical decision making. The subjective variables from the 3PSST could be established to identify RT, TMT and SMT physical function impairment for treatment planning and effectiveness evaluation.