Background: Identifying mobility disability as early as possible in the aging process allows interventions to be introduced before signifcant strength and mobility are lost, leading to better outcomes by delaying the physical deadline which deprives individuals of their independence. The Timed Up From Floor (TUFF) test is a screening test in which the individual is timed transitioning from supine on the floor to the stable, upright stance. The TUFF is functional and quick, yet challenging enough to identfy signs of impending mobility disability potentially earlier than many tests currently in use. To be of use, however, reliability and validity must be established. Objective: To determine reliability and validity of the TUFF test as a screening test to identify early signs of mobility disability in community-dwelling older females. Methods: In this prospective methodological study, 62 community-dwelling females, 55 years of age and older, consented to participate in this study. Inter-rater reliability of the TUFF test was established by comparing the timing results of three raters observing the same videotaped performances. Test-retest reliability was determined by having the same three raters time videos of the same participants performing the TUFF test during session approximately 1 week apart. Participants unable to get up from the floor unassisted had the option of performing a modified TUFF test (mTUFF) which permitted use of a chair to assist with the transition from supine to standing. To establish validity, the association of TUFF test times with the SF-36 questionnaire scores, usual and fast gait speeds, and 30-second sit-to-stand test repetitions was examined. Results: Both TUFF and mTUFF tests were determined to have excellent inter-rater reliability. Test-retest reliability was acceptable with an ICC=0.91 for the TUFF and ICC=0.82 for the mTUFF. The TUFF correlated with the physical function component of the SF-36, usual gait speed, fast gait speed, and the 30-second sit-to-stand test. Limitations: The study was limited to females; therefore, generalizability to males cannot be assumed. Statistical analysis of the mTUFF was underpowered, therefore conclusions cannot be drawn regarding the validity of the mTUFF in this study. Conclusions: The TUFF test is a reliable and valid screening test to identify early signs of mobility disability in community-dwelling female older adults. It is arguably a more physically demanding test than gait speed, suggesting it may identfiy signs of impending mobility disability earlier in the process. The mTUFF will require further testing with a greater number of participants in order to determine validity.