A long-delayed plan to follow the health of 100,000 U.S. children from birth to age 21 is in limbo again, in the wake of a critical outside review. A National Academies panel finds that the National Children's Study has some strong points—but also a host of weaknesses. The panel recommends that the study's leader, the National Institutes of Health's (NIH's) child health institute, make changes to the study's design and management that would likely delay initial recruitment, now planned for 2015. And the price tag that the panel puts on the revamped effort—upward of $1.5 billion—could erode support for the ambitious effort. In response to the report, NIH Director Francis Collins has put the study on hold.