Objective. —To define the growth pattern of girls with Rett syndrome with respect to height, weight, and fronto-occipital head circumference. Design. —Longitudinal with irregular intervals between measurements. Setting. —Rett Syndrome Program Project at Baylor College of Medicine, Houston, Tex. Participants. —Ninety-six girls fulfilling criteria for Rett syndrome; comparison group with standard growth curves. Selection Procedure. —Consecutive entries into the Rett Syndrome Program Project. Intervention. —None. Measurements/Main Results. —Height, weight, and fronto-occipital head circumference data were grouped into intervals. Group medians were then generated. Regression lines were fitted through the median points and plotted on standard growth charts. Deceleration of growth velocities began at age 3 months and persisted through age 18 years. Conclusions. —Early deceleration of head growth, followed by deceleration of weight and height measurements, appears to be a growth pattern characteristic of Rett syndrome. This pattern of growth may provide the earliest clinical indicator for the diagnosis of Rett syndrome. © 1993, American Medical Association. All rights reserved.