Historically, there have been no accounts of an association between simple metopic ridging and the Chiari I malformation. We prospectively evaluated 50 children with simple metopic ridges and found that 30% of these patients had a Chiari I malformation. During the period in which this screening for simple metopic ridges was performed, only 9% of the total patient population (324) was diagnosed as having a Chiari I malformation. We hypothesize that small decreases in anterior fossa volume in children with a simple metopic ridge and no other clinical findings of trigonocephaly may increase their chance of having a Chiari I malformation that becomes symptomatic. In addition, simple metopic ridging should perhaps be added to the list of bony anomalies associated with the Chiari I malformation, such as atlantal assimilation and retroverted odontoid processes. Future studies aimed at calculating anterior fossa volumes in children with a Chiari I malformation and imaging all children with simple metopic ridges are now necessary to ascertain if there is an increased risk of these patients becoming symptomatic with a hindbrain hernia or having a hindbrain hernia, respectively. Copyright © 2001 S. Karger AG, Basel.