Bipolar disorder (BD) adversely affects daily activities/functioning. The Sheehan Disability Scale (SDS) assesses disability in work/school activities, family relationships, and social functioning, and it evaluates the functional impact of psychiatric disorders. BD outpatients from 21 U.S. sites completed a battery of validated instruments (including the SDS) three times over 8-12 weeks. Instrument reliability (internal consistency, test-retest), validity (construct, convergent validity, known groups) and responsiveness were measured. There were missing data for the SDS in 2% of the 225 subjects with BD. One factor explained 82% of the variance. All SDS items had rotated factor loadings on the first factor >0.90, confirming the appropriateness of the SDS total score. Item-scale correlations surpassed 0.40. There was excellent internal consistency reliability for the SDS total score (Cronbach's alpha=0.89). Test-retest reliability was acceptable for the SDS total score (intraclass correlation coefficient=0.73). Correlations with other instruments demonstrate convergent and divergent validity. The SDS total and item scores significantly discriminated between (self-rated) overall health status, clinician-rated functional status, and clinician-rated depression, evidencing known group validity. The SDS demonstrated ability to detect change over time. The SDS is a valid, reliable measure of disability and is responsive to change over time when used in subjects with BD.