Project, an ongoing longitudinal study of nondisabled, community-living persons, aged 70 years or older. After a comprehensive, home-based assessment, participants were categorized into three groups according to their risk for disability (low, intermediate, and high) and were subsequently followed for up to two years with monthly telephone interviews (98% completion rate) to ascertain the presence of disability in four key activities of daily living (ADLs).We compared the rate of ADL disability obtained from a single follow-up assessment with that obtained from monthly assessments for intervals of 6, 12, 18, and 24 months. RESULTS: For any ADL and for each of the four individual ADLs (walking, bathing, dressing, and transferring), the rates of disability at 12 months were at least twice as high for the monthly assessments as for the single follow-up assessment. For any ADL disability, for example, the corresponding rates were 0.22 and 0.10. Although the overall rates were lower, the results for persistent disability, defined as a new disability that was present for at least two consecutive months, were similar. As the length of the assessment interval increased, the``true'' rate of disability, as determined by the monthly assessments, was increasingly underestimated by a single follow-up assessment. For example, the rates of any ADL disability for the monthly and single follow-up assessments were 0.28 and 0.09 at 18 months and 0.37 and 0.11 at 24 months, respectively. While these underestimates of disability were due almost exclusively to high recovery rates for low-risk participants, they were due increasingly to losses to follow-up from deaths for high-risk participants. CONCLUSION: The incidence of disability is substantially underestimated by longitudinal studies with long assessment intervals. These underestimates could lead policy-makers to inaccurately estimate the health care needs of community-living older persons. While adolescents in general face many serious health risks, these youth face worse and more chronic health problems, psychiatric and behavioral problems, alcohol and substance abuse, sexually transmitted diseases (STD) and teen pregnancies. School-based clinics have been reported to improve health among adolescents through increased access. We hypothesized that increased access to medical care within the shelter environment would improve health outcomes in this under served population. METHODS: Homeless youth were surveyed in 1992 and 1998 at the only Denver-area shelter dedicated to youth under 21. The first survey, in 1992, occurred when medical services were provided in the shelter 8 hours per week. At the time of the second survey in 1998, medical services had increased to 36 hours per week. The surveys were of structured interview form based on the Adolescent Health Survey instrument. Outcomes assessed included access to health care, health satisfaction, STD's and pregnancies. RESULTS: The two study samples differed somewhat with regard to demographics. In 1998, there were more males (62%) than in 1992 (55%). There were also substantially more African-Americans (16% vs. 7%). The proportion of African Americans among shelter users was twice the proportion of African Americans in the community.`Good' or`Excellent'; self-reported health increased from 65% to74% between 1992 and 1998. Endorsement of frequent difficulty accessing care decreased from 3 1% to 14% between 1992 and 1998. Agreement with the statement,``the last time I needed healthcare I took care of it myself'' decreased from 24% in 1992 to 8% in 1998. The number of self-reported STD's decreased from 26% in 1992 to 17% in 1998, compared with the 2.4% reported in Colorado high school students in 1996. This decrease was seen at the same time a Centers for Disease Control-sponsored STD screening project was working to reach homeless youth, and detection rates may actually have increased. The number of teen pregnancies decreased from 14% in 1992 to 6% in 1998. CONCLUSION: Among homeless youth, increased access to medical care through increased availability of services in the shelter environment was associated with improvements in perceived health, access to health care, and reductions in some common health problems. Continued expansion of services within the shelter could have a profound impact on problems such as mental health and substance abuse.