Family communication is essential for accurate cancer risk assessment and counseling; family blockers play a role in this communication process. This qualitative analysis of social exchanges is an extension of earlier work characterizing those who are perceived by study participants as health information gatherers, disseminators, and blockers within families with Hereditary Breast and Ovarian Cancer (HBOC) susceptibility. Eighty-nine women, ages 23-56 years, enrolled in a Breast Imaging Study (BIS) and participated in a sub-study utilizing a social assessment tool known as the Colored Ecological Genetic Relational Map (CEGRM). Purposive sampling ensured that participants varied according to numbers of participating family members e.g., ranging from 1 to 6. Eighty-nine women from 42 families (1-8 relatives/family) participated. They collectively designated 65 blockers, both male and female. Situational factors, beliefs, attitudes and cultural traditions, privacy and protectiveness comprised perceived reasons for blocking intra-family health communications. Longitudinal data collected over 4 years showed families where blocking behavior was universally recognized and stable over time, as well as other families where blocking was less consistent. Self-blocking was observed among a significant minority of participating women. Blocking of health communications among family members with HBOC was variable, complex, and multifaceted. The reasons for blocking were heterogeneous; duration of the blocking appeared to depend on the reasons for blocking. Blocking often seemed to involve bi-directional feedback loops, in keeping with Lepore's Social Constraints and Modulation Theory. Privacy and protectiveness predominated as explanations for long-term blocking.