We reexamined field data on cognitive performance in light of recent research that shows open-fire cooking--with its emission of harmful substances--to pose a risk to healthy physical development. Tests of three- to nine-year-old children in four communities around the world yielded evidence concerning block-building skills, memory, and the discernment of embedded figures. Naturalistic observations of these children were also undertaken in everyday settings. Open-fire cooking (as opposed to cooking on kerosene stoves) was associated with both lower cognitive performance and less frequent structured play at all ages. Although these correlational results do not reveal causal mechanisms, they are consistent with ideas about negative developmental consequences of exposure to open-fire cooking and suggest that research is needed on the effect on brain development of practices involving production of indoor smoke.