The notion of risk underlying the concept of vulnerability implies that everyone is potentially vulnerable (or at risk), that is, there is always a chance of developing health problems. The risk is, however, greater for those with the least social status, social capital, and human capital resources to either prevent or ameliorate the origins and consequences of poor physical, psychological, or social health. The completeness and accuracy of information on the health status of the vulnerable populations examined here varies substantially across groups. Methodological work is needed to derive standardized definitions of terms, specify the content and timing for collecting information for minimum basic data sets, and develop uniform standards for evaluating and reporting data quality on the health status of vulnerable populations. The variety of indicators of vulnerable populations examined indicates that during the decade of the 1980s the incidence of serious physical, psychological, and/or social needs increased (at worst) and was unameliorated (at best) for millions of Americans. AIDS emerged as a new and deadly threat from a handful of cases classified as Gay-Related Immune Deficiency in the early part of the 1980s to what now may be over a million Americans who are HIV-positive. The number of homeless has increased an average of 20% a year to estimates now ranging up to one million men, women, or children homeless on any given night to twice that number who may be homeless sometime during the year. Over seven million people immigrated to the United States during the period from 1981 to 1990--an increasing proportion of whom are refugees carrying with them the physical, psychological, and social wounds of war. The number of children abused by family members or other intimates has burgeoned to an estimated 1.6 to 1.7 million per year, and with the greater use of firearms, intentional acts of violence towards oneself or others are becoming increasingly deadly in their consequences. Though fewer Americans smoke, drink, and use illicit drugs in general than was the case earlier in the decade of the 1980s, the use of cocaine (and particularly crack) among hard-core addicts has resulted in increases in the number of drug-related deaths.(ABSTRACT TRUNCATED AT 400 WORDS)