The research reported in this paper seeks to identify and test casual hypotheses of why the undercount (especially of Black males) occurs. Two explanations have been advanced at the Census Bureau to explain the high undercount of Black men: deliberate concealment, and mobile and transient residency patterns. Although these hypotheses are plausible, evidence is sparse and indirect. It is difficult to gain direct evidence about people who deliberately avoid surveys or whose lifestyle leads them to be missed from household- based surveys. However, intensive small-area studies conducted by researchers who live in or are accepted in a neighborhood may tell us a great deal about who is missed in the census, and why, for that small area.