This paper (Part I) and its companion paper (Part II) provide an overview of the primary prevention of child maltreatment. Part I reviews the effectiveness of interventions aimed at the primary prevention of child physical abuse and neglect. Prospective controlled trials published between January 1979 and May 1993 were systematically identified. The quality of each study was determined using criteria which assessed methodological rigor. Interventions aimed at the prevention of physical abuse and neglect were classified into six main categories within the broad group of perinatal and early childhood programs. While many of these programs did not show a reduction in physical abuse or neglect, there is evidence that extended home visitation can prevent physical abuse and neglect among disadvantaged families.