Adequate hygiene behaviors and environmental health conditions are fundamental to children's health, development, and well-being. They are especially important in institutional care settings for orphaned and abandoned children, a particularly vulnerable population whose basic needs are often not met.We systematically reviewed the evidence about hygiene behaviors and environmental health conditions in institutional care settings for children and associated health outcomes; interventions to improve these behaviors, conditions, and outcomes; and obstacles to improvement.PubMed, Web of Science, Scopus, and EBSCOhost were searched for studies in the peer-reviewed and grey literature. Studies were included if they reported primary data on one or more environmental health condition or hygiene behavior in an institutional care setting for orphaned and abandoned children.Forty-five publications reporting on over 500 institutions in 29 countries were included. The most documented concern was poor personal hygiene behaviors followed by inadequate water and sanitation infrastructure and overcrowding. Protozoan, helminthic, viral infections, and diarrheal illness among institutionalized children were the most commonly documented associated health outcomes.More studies documented the status of hygiene and environmental health in children's institutions than interventions to improve behaviors and conditions. Insufficient finances and expertise or involvement of caregivers are reported barriers to implementing improvements in children's institutions. The development of guidelines for essential environmental health standards in orphanages, monitoring of facility conditions, accountability for facility deficiencies, and implementation research to identify improvement opportunities would contribute to and promote the health and development of orphaned and abandoned children worldwide.