In the United States, infants with birthweights <750 g (i.e., extremely low birthweight infants) account for <1% of all births but approximately one third of the total infant mortality rate. Because these infants often have short life spans, their deaths might be misclassified as fetal deaths, leading to an underestimation of the overall infant mortality rate. Accurate infant mortality rates are important for program planning and evaluation, identification of health disparities and emerging trends, and development of prevention strategies. To assess the extent of unregistered deaths among extremely low birthweight infants born in Ohio during January-June 2006, the Ohio Department of Health analyzed birth and death records from this period for all infants with birthweights <750 g (1.7 lbs) and contacted birth hospitals to follow up on the discharge status of these infants. This report describes the results of that analysis, which indicated that 7% of the extremely low birthweight infants who were born in Ohio during this period, and who subsequently died, had deaths that were unregistered. The findings emphasize the need for routine verification of the discharge status of these infants from their birth hospitals and follow-up to ensure proper registration of deaths.