Phase I of the Family Development Study was designed as descriptive epidemiologic case-control study of Children's Hospital patients. "Cases" included a variety of presenting conditions in which it was believed that specific factors affecting the capacity of a family to nurture and protect a child under four years of age might form a common and significant part of their etiology. These included cases of child abuse and neglect, failure to thrive, ingestions and accidents. "Controls" were comparable acute medical conditions matched on age, race, and very roughly on socioeconomic status. The study included 303 children on the inpatient division of the Hospital and 257 outpatients visiting its Emergency Clinic. The data generally support the basic hypothesis that differential levels of the several categories of hypothesized stresses and hypothesized personal and social strengths determine the occurence of "social pediatric illnesses" in the families under study. They indicate that child abuse cases tend to be more extreme on the stress-strength variables than the accidents, ingestions and failures to thrive. More importantly there are a suggestions of differences between the various case categories which point the way toward a set of somewhat distinct pathogenetic mechanisms among several of the case categories. (Author/JM)