Published Lyme meningitis treatment studies are limited by outcome measures that cannot capture day-to-day differences in clinical improvement. Our goal was to use expert consensus to develop a daily measurement instrument for assessing clinical improvement in children with Lyme meningitis. We assembled a panel of 24 nationally recognized Lyme disease experts to develop a pediatric daily symptom measurement instrument. Experts responded to four rounds of surveys, receiving feedback about the previous round prior to each subsequent round with anonymity for participants and responses. Using modified Delphi methods, we established a novel Lyme meningitis outcome instrument. The final Pediatric Lyme Meningitis Symptom Measurement instrument includes five items: headache (Likert scale), neck pain/stiffness (Likert scale), fever (yes/no), light sensitivity (yes/no) and vision problems (yes/no). We defined three consecutive days with a symptom score of zero as the minimum to define clinical improvement. Using expert consensus, we developed a novel Pediatric Lyme Meningitis Symptom Measurement instrument to measure treatment response daily for children with Lyme meningitis enrolled in clinical studies.